Is it safe to use make up powder on your hair after a hair transplant ?

There should be no issue but it is best to check with your doctor who performed your surgery in case there are issue specific to your situation. 

At this point you can use any type of topical concealer you like.You don't have to worry about injuring any of the grafts.

After 4 months your healing process should be finished, so you can do whatever you want to your head and not worry about harming your grafts any more than you'd worry if it was normal hair. Unless your doctor has indicated otherwise or for some reason your healing process was delayed there's no reason to worry. Asking your doctor can't hurt.

On the 8th day after surgery  you are safe to use make up and conceal powder without any harm to hair follicle. Be patient and you should start to see growth in approximately 3 months.

After four months topical products should not be a problem.  It wouldn't hurt to run the name of the product by your surgeon to assure he/she agrees.

Once all of the crusts have left, you can use make-up without any worry. You are now normal and need to wait out the growth