This short video gives two suggestions for writing on pages when they’re in sheet protectors:
Take the page out to write on it, then put it back in its sheet protector pocket
Write your note on a post-it, then put that on top of the sheet protector
If for some reason, these aren’t doable, there’s one more option not mentioned in the video.
Although trifold and bifold sheet protectors make for easier music change-outs, the ChoreoKeeper binder can be used without them. (You’d need to tape 2-3 pages together to take advantage of the clips.) Using the binder without sheet protectors means that your music pages are always exposed.