I want to know if this can be done for games like Kirby's Dream Land 1 & 2, to force their GBC palettes all the time, perhaps Donkey Kong for GB could be modified as well to force the GBC/SGB palette every single time as well.
The GBC palettes for (well, most of the Nintendo GB games) are coded into the GBC boot ROM. The boot ROM detects those games and loads the default palette if it doesn't find one. So you need to set up the emulator to run the boot ROM before the game and in theory it should work regardless of extension if you force GBC mode as well. No ROM hacking needed.
For dual-compatible games, they can detect which hardware they are running on by the value in A as the game boots (the GB/GBC boot ROMs write a different value to disable the boot ROM as an additional sign to the game what hardware they are on).
If you want SGB, then force SGB in your emulator. If you're thinking of hacking the game to force SGB because you want to play the hacked ROM on a flashcart or something on real hardware, I think SGB palettes are applied on the SNES side.
If you want to do what Pokemon Yellow did and use SGB palettes on the GBC well then you have a lot of per-game ASM hacking work ahead of you. Pretty much the same as any "colorization" hack.