@masoftware so :

documentation is obsolete uae system per game basis seems broken if you want to modify systems files, you need to remount partition as write, in SSH : mount -o remount, rw / or what you can do is add a single .uaeconfig.uae file inside the roms folder for the system you use (either amiga600 or amiga1200) containing what you want to modify, it should work. Maybe in a subfolder of the rom folder you also need to add it.