Can you refrigerate leftover cheesecake filling and use it later (within a few days)

If you're going to use it within a few days anyway, why not just make another cheesecake with the filling now? The unbaked filling will be iffy a few days later, but a baked cheesecake lasts practically forever in the fridge, and gets better every day!

Certainly the next day, but I wouldn't go beyond that. The proteins will begin to break down, and you'll lose some of their thickening power.