Can I keep my rounded hairline after a forehead lowering?

When you make an incision to pull the hairline forward, it is a straight line and when you pull it, it tends to get straighter. You have a nice hairline shape, and without a side view it is hard to know if hairline advancement makes much sense.
We do a lot of feminization hairline and hair grafting. Likely I'd suggest hair grafts as a better option for you.

When incision along the hairline is properly planed it is very likely that patient will maintain the natural hairline. This should be discussed with your surgeon ahead of time. Good luck.