Stock OS compared to what? A hybrid OS? All OSs that come from a carrier - any carrier - is technically "stock". They are all the same and only your particular branded phone determines which carrier specific features are loaded. There's nothing for you to "rename".
You really need the latest build. Your carrier may have all builds they released going back to the earliest they had when they released the phone (AT&T does, for example) but you really don't want the really old builds because there where issues with them.
Who is your carrier?