How can I deactivate bad RAM regions on a Macbook Pro (Retina 13")?
Tho it is possible in Linux and Mac O/S X is in fact a UNIX-based operating system I am not aware of a way to do this in Mac O/S X.

As for your particular Mac, I believe that the RAM is non replaceable (EG soldered to the system board). So if it is out of warranty and you did not extend the warranty with Applecare a system board replacement would not be cheap.

If you have a local Apple store you can make a Genius appointment and they will diagnose your issue and advise you what can be done at no charge.