diff --git a/tests/HDF5WritingTest.cpp b/tests/HDF5WritingTest.cpp
index 6576e78c..23be0d97 100644
--- a/tests/HDF5WritingTest.cpp
+++ b/tests/HDF5WritingTest.cpp
@@ -13,6 +13,64 @@
 
 using namespace std::literals::chrono_literals;
 
+TEST_CASE("HDF5Group_create_reopen_and_fail", "[HDF5][Unit]") {
+    {
+        HDF5File file("scratch_group_reopen.h5");
+
+        REQUIRE_NOTHROW(HDF5Group(file, "/group1"));
+        REQUIRE(file.Exists("/group1"));
+
+        REQUIRE_NOTHROW(HDF5Group(file, "/group1"));
+        REQUIRE(file.Exists("/group1"));
+
+        REQUIRE_THROWS(HDF5Group(file, "/missing_parent/group2"));
+    }
+
+    remove("scratch_group_reopen.h5");
+    REQUIRE(H5Fget_obj_count(H5F_OBJ_ALL, H5F_OBJ_ALL) == 0);
+}
+
+TEST_CASE("HDF5Attr_string_update", "[HDF5][Unit]") {
+    const std::string first_value = "abc";
+    const std::string second_value = "a much longer attribute value";
+
+    {
+        HDF5File file("scratch_attr_string_update.h5");
+        REQUIRE_NOTHROW(file.Attr("str_attr", first_value));
+        REQUIRE_NOTHROW(file.Attr("str_attr", second_value));
+    }
+
+    {
+        HDF5ReadOnlyFile file("scratch_attr_string_update.h5");
+        REQUIRE(file.ReadAttrStr("str_attr") == second_value);
+    }
+
+    remove("scratch_attr_string_update.h5");
+    REQUIRE(H5Fget_obj_count(H5F_OBJ_ALL, H5F_OBJ_ALL) == 0);
+}
+
+TEST_CASE("HDF5Attr_int64_update", "[HDF5][Unit]") {
+    const int64_t first_value = -1234567890123LL;
+    const int64_t second_value = 9876543210123LL;
+
+    {
+        HDF5File file("scratch_attr_int64_update.h5");
+        REQUIRE_NOTHROW(file.Attr("int_attr", first_value));
+        REQUIRE(file.ReadAttrInt("int_attr") == first_value);
+
+        REQUIRE_NOTHROW(file.Attr("int_attr", second_value));
+        REQUIRE(file.ReadAttrInt("int_attr") == second_value);
+    }
+
+    {
+        HDF5ReadOnlyFile file("scratch_attr_int64_update.h5");
+        REQUIRE(file.ReadAttrInt("int_attr") == second_value);
+    }
+
+    remove("scratch_attr_int64_update.h5");
+    REQUIRE(H5Fget_obj_count(H5F_OBJ_ALL, H5F_OBJ_ALL) == 0);
+}
+
 TEST_CASE("HDF5DataSet_scalar", "[HDF5][Unit]") {
     uint16_t tmp_scalar = 16788;
     {
diff --git a/writer/HDF5Objects.cpp b/writer/HDF5Objects.cpp
index 0861a4db..7ed7a77d 100644
--- a/writer/HDF5Objects.cpp
+++ b/writer/HDF5Objects.cpp
@@ -315,76 +315,119 @@ void HDF5Fapl::SetVersionTo1p10orNewer() {
     H5Pset_libver_bounds(id, H5F_LIBVER_V110, H5F_LIBVER_LATEST);
 }
 
+template <typename T>
+static HDF5Object& WriteOrCreateScalarAttr(HDF5Object& object, const std::string& name, const T& val) {
+    HDF5DataSpace dataspace;
+    HDF5DataType datatype(val);
+
+    hid_t attr_id = -1;
+
+    if (H5Aexists(object.GetID(), name.c_str()) > 0) {
+        attr_id = H5Aopen(object.GetID(), name.c_str(), H5P_DEFAULT);
+        if (attr_id < 0)
+            throw JFJochException(JFJochExceptionCategory::HDF5, "Cannot open attribute " + name);
+
+        hid_t existing_type = H5Aget_type(attr_id);
+        if (existing_type < 0) {
+            H5Aclose(attr_id);
+            throw JFJochException(JFJochExceptionCategory::HDF5, "Cannot get attribute type " + name);
+        }
+
+        const bool recreate =
+                (H5Tget_class(existing_type) != H5Tget_class(datatype.GetID())) ||
+                (H5Tget_size(existing_type) != H5Tget_size(datatype.GetID()));
+
+        H5Tclose(existing_type);
+        H5Aclose(attr_id);
+
+        if (recreate) {
+            if (H5Adelete(object.GetID(), name.c_str()) < 0)
+                throw JFJochException(JFJochExceptionCategory::HDF5, "Cannot delete attribute " + name);
+
+            attr_id = H5Acreate2(object.GetID(), name.c_str(), datatype.GetID(), dataspace.GetID(), H5P_DEFAULT, H5P_DEFAULT);
+        } else {
+            attr_id = H5Aopen(object.GetID(), name.c_str(), H5P_DEFAULT);
+        }
+    } else {
+        attr_id = H5Acreate2(object.GetID(), name.c_str(), datatype.GetID(), dataspace.GetID(), H5P_DEFAULT, H5P_DEFAULT);
+    }
+
+    if (attr_id < 0)
+        throw JFJochException(JFJochExceptionCategory::HDF5, "Cannot create/open attribute " + name);
+
+    herr_t ret = H5Awrite(attr_id, datatype.GetID(), &val);
+    H5Aclose(attr_id);
+
+    if (ret < 0)
+        throw JFJochException(JFJochExceptionCategory::HDF5, "Attribute write unsuccessful");
+    return object;
+}
+
 HDF5Object & HDF5Object::Attr(const std::string &name, const std::string &val) {
     HDF5DataSpace dataspace;
     HDF5DataType datatype(val);
 
-    hid_t attr_id = H5Acreate2(id, name.c_str(), datatype.GetID(), dataspace.GetID(), H5P_DEFAULT, H5P_DEFAULT);
+    hid_t attr_id = -1;
+
+    if (H5Aexists(id, name.c_str()) > 0) {
+        attr_id = H5Aopen(id, name.c_str(), H5P_DEFAULT);
+        if (attr_id < 0)
+            throw JFJochException(JFJochExceptionCategory::HDF5, "Cannot open attribute " + name);
+
+        hid_t existing_type = H5Aget_type(attr_id);
+        if (existing_type < 0) {
+            H5Aclose(attr_id);
+            throw JFJochException(JFJochExceptionCategory::HDF5, "Cannot get attribute type " + name);
+        }
+
+        const bool recreate =
+                (H5Tget_class(existing_type) != H5T_STRING) ||
+                (H5Tget_size(existing_type) < val.length() + 1);
+
+        H5Tclose(existing_type);
+        H5Aclose(attr_id);
+
+        if (recreate) {
+            if (H5Adelete(id, name.c_str()) < 0)
+                throw JFJochException(JFJochExceptionCategory::HDF5, "Cannot delete attribute " + name);
+
+            attr_id = H5Acreate2(id, name.c_str(), datatype.GetID(), dataspace.GetID(), H5P_DEFAULT, H5P_DEFAULT);
+        } else {
+            attr_id = H5Aopen(id, name.c_str(), H5P_DEFAULT);
+        }
+    } else {
+        attr_id = H5Acreate2(id, name.c_str(), datatype.GetID(), dataspace.GetID(), H5P_DEFAULT, H5P_DEFAULT);
+    }
+
+    if (attr_id < 0)
+        throw JFJochException(JFJochExceptionCategory::HDF5, "Cannot create/open attribute " + name);
+
     herr_t ret = H5Awrite(attr_id, datatype.GetID(), val.c_str());
     H5Aclose(attr_id);
 
-    if (ret < 0) throw JFJochException(JFJochExceptionCategory::HDF5, "Attribute write unsuccessful");
+    if (ret < 0)
+        throw JFJochException(JFJochExceptionCategory::HDF5, "Attribute write unsuccessful");
     return *this;
 }
 
 HDF5Object & HDF5Object::Attr(const std::string &name, int32_t val) {
-    HDF5DataSpace dataspace;
-    HDF5DataType datatype(val);
-
-    hid_t attr_id = H5Acreate2(id, name.c_str(), datatype.GetID(), dataspace.GetID(), H5P_DEFAULT, H5P_DEFAULT);
-    herr_t ret = H5Awrite(attr_id, datatype.GetID(), &val);
-    H5Aclose(attr_id);
-
-    if (ret < 0) throw JFJochException(JFJochExceptionCategory::HDF5, "Atrribute write unsucessful");
-    return *this;
+    return WriteOrCreateScalarAttr(*this, name, val);
 }
 
 HDF5Object & HDF5Object::Attr(const std::string &name, uint32_t val) {
-    HDF5DataSpace dataspace;
-    HDF5DataType datatype(val);
-
-    hid_t attr_id = H5Acreate2(id, name.c_str(), datatype.GetID(), dataspace.GetID(), H5P_DEFAULT, H5P_DEFAULT);
-    herr_t ret = H5Awrite(attr_id, datatype.GetID(), &val);
-    H5Aclose(attr_id);
-
-    if (ret < 0) throw JFJochException(JFJochExceptionCategory::HDF5, "Atrribute write unsucessful");
-    return *this;
+    return WriteOrCreateScalarAttr(*this, name, val);
 }
 
 HDF5Object & HDF5Object::Attr(const std::string &name, int64_t val) {
-    HDF5DataSpace dataspace;
-    HDF5DataType datatype(val);
-
-    hid_t attr_id = H5Acreate2(id, name.c_str(), datatype.GetID(), dataspace.GetID(), H5P_DEFAULT, H5P_DEFAULT);
-    herr_t ret = H5Awrite(attr_id, datatype.GetID(), &val);
-    H5Aclose(attr_id);
-
-    if (ret < 0) throw JFJochException(JFJochExceptionCategory::HDF5, "Atrribute write unsucessful");
-    return *this;
+    return WriteOrCreateScalarAttr(*this, name, val);
 }
 
 HDF5Object & HDF5Object::Attr(const std::string &name, uint64_t val) {
-    HDF5DataSpace dataspace;
-    HDF5DataType datatype(val);
-
-    hid_t attr_id = H5Acreate2(id, name.c_str(), datatype.GetID(), dataspace.GetID(), H5P_DEFAULT, H5P_DEFAULT);
-    herr_t ret = H5Awrite(attr_id, datatype.GetID(), &val);
-    H5Aclose(attr_id);
-
-    if (ret < 0) throw JFJochException(JFJochExceptionCategory::HDF5, "Atrribute write unsucessful");
-    return *this;
+    return WriteOrCreateScalarAttr(*this, name, val);
 }
 
 HDF5Object & HDF5Object::Attr(const std::string &name, double val) {
-    HDF5DataSpace dataspace;
-    HDF5DataType datatype(val);
-
-    hid_t attr_id = H5Acreate2(id, name.c_str(), datatype.GetID(), dataspace.GetID(), H5P_DEFAULT, H5P_DEFAULT);
-    herr_t ret = H5Awrite(attr_id, datatype.GetID(), &val);
-    H5Aclose(attr_id);
-
-    if (ret < 0) throw JFJochException(JFJochExceptionCategory::HDF5, "Atrribute write unsucessful");
-    return *this;
+    return WriteOrCreateScalarAttr(*this, name, val);
 }
 
 HDF5Object & HDF5Object::Attr(const std::string &name, const std::vector<double> &val) {
@@ -632,14 +675,19 @@ HDF5Group::HDF5Group(const HDF5Object& parent, const std::string &name) : HDF5Gr
 }
 
 HDF5Group::HDF5Group(const HDF5Object& parent, const char *name) : HDF5Object() {
-    id = H5Gcreate(parent.GetID(), name, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
+    if (H5Lexists(parent.GetID(), name, H5P_DEFAULT) > 0)
+        id = H5Gopen(parent.GetID(), name, H5P_DEFAULT);
+    else
+        id = H5Gcreate(parent.GetID(), name, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
+
+    if (id < 0)
+        throw JFJochException(JFJochExceptionCategory::HDF5, "Cannot open/create HDF5 group " + std::string(name));
 }
 
 HDF5Group::~HDF5Group() {
     H5Gclose(id);
 }
 
-
 HDF5File::HDF5File(const std::string& filename, bool v1_10) : HDF5Object() {
     HDF5Fapl fapl;