Hey fellow devs.  I like having my OSX version signed so that when people download it directly they can just run it:

https://itch.io/docs/itch/integrating/platforms/macos.html

BUT I'd like to not have to rebuild, archive, export and resign my OSX version every time I add/change a text file or whatever. 

Can we just add new resource files to an OSX app and upload with butler, or will that break some hash tag / verification in the  signed Apple package?

I'm not sure but I'm guessing it would break the signature since the signature is there to verify the integrity of the executable's files. Any unsigned changes would be an indicator for tampering with the executable.