I think it partly depends on what kind of HRT drugs you're on.
For instance, estrogen may not have much (if any) effect on restoring hair loss, spiro may have some effect since you're reducing testosterone (the main culprit), but finasteride (a DHT blocker) is actually prescribed to genetic males for hair loss. So, once you work out what drugs you'll be taking and whether or not there's anything else you should be using (minoxidil, etc...) and have let that run it's course (a year?) to see how any of it affects your hairline, THEN you can start thinking about surgery for hair loss.
At least, that's my opinion/understanding. Medication is less invasive and you never know how they or hormones will actually affect you until you start taking them and have been on them for a while.
Talk with your HRT doctor and explain these concerns and they'll probably start you on drugs more specifically tailored to this need instead of something else for instance.
