Thanks so much for this RandomityGuy! In particular, I want to say how glad I am that you've made it an option to switch between old and new spawns. I'd love to see an expanded version of this in PQ too! Which maps does this affect? Is it only official levels that have had their spawns changed since 2017 (Triple Decker, Maximo Center, Marble Agility Course, Basic Agility Course, All Angles, Marbleland, Battlecube Revisited, Lupus, Par Pit, Eye of the Storm, Nadir, Spires—this list is just from memory, so it might be wrong)?
I noticed by playing Marble Agility Course that the gem hitboxes (at least in that level, but potentially all hitboxes throughout the game) are a little lenient—I could get the yellow gem on top of the large tunnel through the ceiling, and I could also get the yellow gem on top of the inverted half-pipe thing through the ceiling. The gems on the little wooden... half-dowels (for lack of a better term) which are suspended between the two brown walls are also very easy to collect just by jumping underneath them. This isn't too big of an issue though—I'd rather have the gems a little easier to collect than much harder to collect like they were originally with this port.
Also, one bug I found: if you select Advanced as the difficulty, then whichever difficulty you were on prior to Advanced will not appear in the choices for difficulty. For example, if you select Custom and then Advanced, Advanced will show up in the place where Custom was, separated from Beginner and Intermediate by a divider, and Custom is nowhere to be seen until you select a different difficulty. I think it should always give you the options of Beginner, Intermediate, Advanced, and Custom no matter which difficulty you're on.