From what I have seen- yes, but you don't need to.
In other words - if you install one, then the other, the executable for the first SSMS remains on the machine, but the icons are pointed to the most current SSMS. Which is good, since you can manage both versions from the same SSMS.
----------------------------------------------------------------------------------
Your lack of planning does not constitute an emergency on my part...unless you're my manager...or a director and above...or a really loud-spoken end-user..All right - what was my emergency again?