I manually set up a collection of save files on PC that start just before all of the level entrances, and separate ones for Boss practice.

For each save, the player owns whatever magic spells would have been available by that point, as well as an amount of money that would make sense for that portion of the game.

The saves are text files, and you can edit certain variables such as keys held, money owned, how strong Skully's sword attack is, etc. You cannot edit the game physics such as jump height or run speed (thankfully).

Is an IL category viable here or are there potential issues? The folder setup I have is super simple and only requires the player to copy/paste the save they want to use into the main Save folder.

I think an IL category is something we can get set up if the files are easy to set up. I can work on making it a category tomorrow.

I'll send you a DM on Twitter with a link to the saves and how I've structured them on PC. Pretty simple but I'll leave it to your judgment :)