@rom Yeah, I don't want to put words in @manton's mouth, but I think we should look at plug-in-based themes as "still in beta". 😊 Customizing does not work the same as with "classic themes". Yet.

But it is possible to modify templates in plug-in-based themes. In more than one way, actually. For example, you can go to DesignEdit Custom Themes and click on the theme in question. From there, you can edit any template you want (or create new ones).

Another approach is to create a new plug-in and, from there, create a new template that overrides the template in the original theme plug-in. Finally, a third way is to duplicate the original theme and make your changes there.

They all feel a bit "hacky", and I hope there will be a more straightforward, official way to customize plug-in-based themes in the future.