Been working on a fully featured celeste save file editor since none exist right now (that I know of).
Almost to the point where I would call it feature complete, though the UI is pretty bad right now. Going to do a pass later to actually make the ui decent. Egui is pretty nice for quick development but, in my experience, making something that looks good is not the easiest thing to do.
As with pretty much all my projects you can find the code on my github. Theres also a library there to r/w saves and a few functions to help work with them.