Can I get my forehead augmented with bone cement 6 months after hair transplant?

If you are considering surgery it would be best to discuss your options with a doctor.  You need to explain to your doctor your goals and expectations.  The doctor needs to examine the area to give you a better assessment.

You can proceed with this procedure and  should not wait longer. Yes, all the grafts are secure and nothing would affect the outcome of the hair transplant. 

To reduce a brow bone, you need to find a doctor who does this. Maxillofacial surgeons often offer this option.