Let's say you have 4 or 5 recruits considering you for only 3 spots. Normally, I would inform of redshirt plans to get someone to stop considering me, but what if that doesn't work? I can withdraw a scholarship offer, but still want to be able to sign him if plan A doesn't work out. If you withdraw an offer, can you offer it back and have him consider you again?

yes

ETA: withdrawing offer does have a negative recruiting impact though- some additional effort may be required...