[borkmaster]

How difficult would it be to create a hack/improvement for Donkey Kong 64 to allow for changing to a different Kong on the fly, or does this already exist somewhere? I've had the itch to run back through this game lately, and would really love to have this QoL improvement available. Thanks!

[Jorpho]

Enormously difficult, mostly likely – especially since it's apparently so complex that even Rare had serious problems with the game crashing.

Not the sort of thing you can knock out in a weekend starting with zero N64 development experience.

[FAST6191]

For many games a character swap in a game with such things in the normal mechanics is nothing terribly drastic and is usually a value somewhere, however some games do have troubles and you have to start initialising things and what have you and if you have not unlocked the characters yet then even more fun. If Jorpho reckons it will be one of the harder ones for that or other reasons I have no reason to doubt here, indeed I recall the game being a bit janky even by ambitious N64 game standards.

Looking at http://doc.kodewerx.org/hacking_n64.html there are some fairly nice cheat options but not as many as I would like for this if you were thinking cheats rather than full bore hack.

Instead you may want to come the other way and make a button activated teleport cheat. Make the game teleport you/rapid speed you to a swap pad and have it handle it all itself.