Is there a particular reason why you don’t want to use a child theme? Child themes are the best way to customize templates when no hook base is provided.

While you cannot change a specific template element from a plugin if no hook base is provided, you can override the loading of the entire template file from a plugin with the “template_include” filter. As long as you return a full path to the replacement file, it can reside anywhere on the server.

thanks for your answer.
I was thinking about using a child theme, but wanted to find a better solution. Am going to take a closer look at the related template to search for the hook. If not successful overriding the template with “template_include” seems to be the way I’ll do it.
In the past I was able to implement all changes without being afraid of loss through updates just with that plugin (theme-customisation-master by James Koster). This way I learned a lot about the general structure of wordpress, but as you can see there is still so much to learn. ??

Best regards,
-Bj?rn