The paper may get gummed up a little. It should not be too bad if the paint has had time to get hard. If the paper does get gummed up, just change the paper. You can tell when the paper is gummed up because the paint will not come off as dust. It will come off as strings.
For what it's worth, I cut a sheet of sandpaper into quarters and find a scrap of wood that's a little smaller for a block. I want a sanding block surface that is hard and flat. I got a couple of the hard rubber sanding blocks but I use a scrap of wood more often than not.