I would add to a_in_the_b's comments:
1) Yes, cancel the notice of redshirt and send some other recruiting action (you may need to re-offer the schollie, I forget);
2) I'm not sure what you're asking, but, if he signs, then you can try to redshirt him anyway;
3) Some reject it (i.e. huge WE hits), some accept with only very small WE hits, others will accept it after a few tries;
4) Your scouting trips will give you info. in messages like: "$20 bill"; "rides the bus", "in a blowout, asked to come out so a senior could play"; "still cheering"; etc. Some messages are meaningless, but I have had good luck getting those recruits to accept a redshirt after signing.
I've given up on informing of redshirt; it's too negative. Some have posted that you need to send it with at least 2 home visits to get the recruit to accept it. I doubt I'll do it again until DI, when the recruiting budgets are high enough to justify it.