So that's not going to be much fun for the user producing different graphics
Still, such a program with set options sounds easy since the grunt work is done.
I did one to patch firmware files for Garmin handheld GPS units where their interface
provides no option for custom intro screens/wallpapers,
but that was 8-16 bit bitmaps... from there, I checked the image the user provided was
of the expected dimensions, bit depth, etc.
Like I said though, in the case of an emulator, a program pretending to be an Amiga,
I think it's contrary to customise the emulated Amiga that way.
I took a quick look at 3.1, and can see only some things clear.. intuition and fonts look the same.
I see a hammer head.. don't know what that's for?
If you have a real Amiga, I think a patch program would def be a winner.