Nope, at least officially as I because Ubi$oft stopped supporting Assassin's Creed: Revelations (AC:R) a looong time go[www.ubisoft.com].

Meaning, that without messing with the AC:R's files the Multi-Player (MP) mode was removed a while back in an Ubi$oft Connect's 'update' even if AC:R is still being sold.

Edit add note: Just noticed that even AC:R's Steam Store page now has a warning in a reddish frame telling that Ubi$oft stopped supporting the MP mode.