Yes and no. If you choose to do a restore from your computer, iTunes will force you to update to the latest iOS due to a jailbreaking issue.
However, a loophole that I use all the time still exists AND, you can keep your iOS version!
.
If you Whipe your 4S (from the option from your phone without tethering it), it does not update YET. The iOS 6.1.3 stays on there till. this criteria is met.
1. You are tethered and iTunes is connected.
2. internet is on
If those criteria is met, iTunes will force you to update.
However, by
a. restoring to factory setting on your phone,
b. turn off wifi on your PC,
c. plug your apple device in...
iTunes will try to update it to the latest version, fail and, give you your beloved iOS version back which can be used for a restore point!
I have also done this with a loaner iPad 2 when mine was in the shop. Opened it up and, was full of joy for being my fav iOS
. Restore went well too
My last word of advice is that you cannot restore from a backup when it was synced with a higher iOS than the one you are running now (eg Backup was from a iOS 7 iPad Air) and, you are trying to restore that iPad air's backup onto a iPad 2 running 6.1.3.