It seems like there might be conflicting code trying to do the same thing, and what takes priority is changing when the game is opened and closed.
It's odd how after resetting the song, you have to close the game twice, for the song to change at the splash screen.
EDIT: Checked again, and it's randomly picking between the 2 songs at the splash screen. So most likely conflicting code trying to do the same thing, with what gets priority being randomized.
PS: I'm glad that your mod is added back to the OP on the game's main thread.
Well, I've been fighting this damn music player's code like an MMA main event.
Come to find out Pink's base code is wonky, even after VN restart. I went to a wiped PC and installed just the base VN. Went into Music and made the first song the new Startup (Waiting to Escape). Then regardless of VN restart or not when one loads a random number of previous saves most of them carry the damn Main Menu song into them (which is not correct). If you then revert to the new original Main Menu default (Over the Horizon) then restart the VN, checking those exact old saves play their respective scene's in-game music proper.
No matter what, even with unmodded the Player must restart the VN for the Main Menu to change correctly to the Startup choice made by the Player. So, it's fucked up right off the bat imho.
In other words I think I'm pissing against the wind here. I'd have to fix the VN's music player proper then mod it. I might just mod what is already there. They'd both behave the same way if one changes the Startup song but at least I can fix the Splash screen issue (which I already found).
Too much time invested over the dev's wonky code on this particular issue.
