Is it alright to perform back of head augmentation with PMMA bone cement 2 months after hair transplant?

If you are considering a cosmetic surgery it would be in your interest to see a doctor for an examination.  
Your doctor can tell you if it is "ok" to have the surgery (after an examination).

Most likely not a problem as far as the grafts growing goes.  However, you may still want to discuss this with your hair transplant surgeon- if you have surgery with foreign material placed in the occiput, it may be unwise to perform further transplant surgery for fear that the cement could become exposed and/or infected during the harvest. 

At 2 months your hair transplant is healed so you can do whatever other sugery you wish to address your other concerns