For your 4S you can't restore back to 5.0.1. You can only go to 5.1. Apple stop signing for 5.0.1 already.
R-Sim some claim can but never try before coz the baseband if different and i don't have a 4S with 5.1 to test. Will let you know if i manage to try on one.
I have Gevey Ultra S coming.

1) if i'm not mistaken, the rules about can only upgrade to iOS 5.1 now because Apple stopped signing iOS 5.0.1 only applies to A5 devices. iPhone 4S and iPad 2. also maybe including the new iPad.
= so probably you can downgrade.

2) again if i'm not mistaken, starting from iOS 5, you cant easily downgrade or upgrade. it depends on currently which iOS is Apple still signing.
= so since you already go up to iOS 5.1, probably you can't downgrade now, too late. Apple not signing iOS 5.0.1 already. not to mention u also have no SHSH saved.

hope others can clarify, TQ.