Now the editor can properly handle without a restart when an already existing PropData gets re-serialized with the scene conversion tool.

editor/prop_editor_plugin.cpp

@@ -65,15 +65,20 @@ void PropEditorPlugin::convert_scene(Node *root, const String &path) {
 
 	ResourceLoader l;
 	if (l.exists(path)) {
-		Ref<Resource> res = l.load(path);
+		Ref<PropData> res = l.load(path, "PropData");
 
-		ERR_FAIL_COND((res.is_valid() && res->get_class() != "PropData"));
+		ERR_FAIL_COND(!res.is_valid());
+
+		res->copy_from(data);
+
+		ResourceSaver s;
+		s.save(path, res);
 
 		res.unref();
+	} else {
+		ResourceSaver s;
+		s.save(path, data);
 	}
-
-	ResourceSaver s;
-	s.save(path, data);
 }
 
 void PropEditorPlugin::_quick_convert_button_pressed() {

props/prop_data.cpp

@@ -112,6 +112,20 @@ void PropData::add_textures_into(Ref<TexturePacker> texture_packer) {
 }
 #endif
 
+void PropData::copy_from(const Ref<PropData> &prop_data) {
+	_id = prop_data->_id;
+	_snap_to_mesh = prop_data->_snap_to_mesh;
+	_snap_axis = prop_data->_snap_axis;
+
+	_props.clear();
+
+	for (int i = 0; i < prop_data->_props.size(); ++i) {
+		_props.push_back(prop_data->_props[i]);
+	}
+
+	emit_changed();
+}
+
 PropData::PropData() {
 	_id = 0;
 	_snap_to_mesh = false;
@@ -144,4 +158,6 @@ void PropData::_bind_methods() {
 #if TEXTURE_PACKER_PRESENT
 	ClassDB::bind_method(D_METHOD("add_textures_into", "texture_packer"), &PropData::add_textures_into);
 #endif
+
+	ClassDB::bind_method(D_METHOD("copy_from", "prop_data"), &PropData::copy_from);
 }

props/prop_data.h

@@ -42,7 +42,6 @@ SOFTWARE.
 
 #include "prop_data_entry.h"
 
-
 #if TEXTURE_PACKER_PRESENT
 #include "../../texture_packer/texture_packer.h"
 #endif
@@ -74,6 +73,8 @@ public:
 	void add_textures_into(Ref<TexturePacker> texture_packer);
 #endif
 
+	void copy_from(const Ref<PropData> &prop_data);
+
 	PropData();
 	~PropData();