Actually sideloading is not a made-up term. It's an existing term, that was (20yrs ago) used regarding to cracks and trainers software. Sideloaders loaded (mainly in DOS but Atari had it too) the main executable along with additional program, a routine or interrupt that would allow disabling of copy protection, cheat on the amount of lives, energy in games (trainers) or simply do something more like play demo music before the game's proper launching. One example - prehistorik game that was distributed by pirates with a "pretrain.com" which allowed to select unlimited lives and sideloaded this routine along with the main program, that would periodically check the counters and keep them up.

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Apparently after checking this term in the internet, I am not so sure that this process had been called this way. Maybe I'll leave it here to provoke a correct answer according to the internet rule #1 - to learn what is the correct answer, just post an incorrect answer in the internet and wait