hey Josue,
thx- I would only use the various settings in the backend for shaping the theme – I assume this will not change those core files, right (I am not an expert, sorry :-)?

Just to make everything right, my procedure for updates w/o loosing a.m. customization would then be:
Adjusting the layout in current version
exporting the theme setting file
install updates – as well valid for both theme and WP updates? –
import theme setting file

Regards Tilman