ParaView does not allow to extend a proxy definition nor to change a property default value in an xml plugin
ParaView does not allow to extend a proxy definition nor to change a property default value in an xml plugin. It is actually possible to do that by copying the full proxy and changing adding from here.
However this is not a really good way of doing it, as all the copied property may break at some point if keeping paraview up to date, and new property added to paraview will not be automatically added.
I personally this feature would be a great one, and would allow lots of other to personalize paraview to their usage, even with the release, without any C++ knowledge needed.