I have redshirted many sophomores. It helps if you are very deep at his position (I think) - if he isn't going to get a lot of minutes some kids figure it out...of course there is a chance he'll tell you how upset he is yadda yadda...worst case, you remove the redshirt everything goes back to normal - no permanent damage.
If he doesn't take it at first, many coaches say that you can remove and reapply it and he will sometimes (often?) take it. This used to work for me, but I've not been able to get to happen for quite a while. I even sat a kid on the bench all season once and tried to apply it the last day before end of season. Still wouldn't take. Then I made the mistake of thinking his WE would recover over off season, and of course it didn't. In fact, kid cam back as a RS Sophomore with a 1 WE. I had to cut him...