I just read up on that a little and as far as I can tell it is either not possible at all or requires lots of modifications besides switching the chips. I couldn’t find a single article so my assumptions are based on the looks of internals. The first backlit GB is the GB Advance SP(I think?) whose internals are far more sophisticated than those of older GBs(especially GBC and DMG). The chips themselves seem to have more pins / chip and are smaller overall.

I also learned that some chiptuners prefer the GBC despite a somewhat worse sound quality as it is more crash-resistant when playing complicated songs. None of them have mentioned a chip switch as the ultimate solution. So I guess that confirms my assumptions.

Regarding your second sentence… other than a backlit panel(which can be added), there is not much to call „worse“ in older machines, at least regarding music production. They are thicker, comparing the size to other DJ equipment, even the DMG looks rather small, shouldn’t be a problem. Batteries can be changed to rechargeable ones, there are mods which make it possible to charge your GB with USB C. The only issue I can see is screen size, but that’s something a musician can live with I think. My stepdad plays Tetris on his DMG while taking no 2 in spite of bad eyesight lol