Thanks for your input.
unfortunately, that approach does not work in this case.
The approval app is a standard app, so I can't change the script tags.
On top of that: the approval app has been written in such a spaghetti entwined manner, that both local resources, as global resources, use the same base path. So if I change the bootstrap path to 1.14/resources/core... in debug mode, the local resources also attempt to follow that path, which doesn't exist, so I get a 404 on those resources.
I thought of renaming the folders for the other versions to something like 'disabled-v1.20' just to try it out, but because it's a SAP standard folder, I can't rename it either...
If there are any other ideas I can try, I'm happy to hear them.