Since TemplateData allows the use of the "inherits" field, the TemplateData editor should have a field where the user can set a "parent" parameter for the "inherits" field.
Topic on Help talk:TemplateData
@Mvolz (WMF), do you maintain the GUI tool, or is that @Mobrovac-WMF or someone else? Developers/Maintainers doesn't have any names.
I think the editing team as a whole is the maintainer, but I've never contributed to it.