Is it possible to get a forehead reduction but still have edges afterwards?

Forehead reduction usually does not involve preserving baby hairs.  If you are considering such surgery it is best to consult with a doctor for what is involved.

A forehead
reduction should be performed with a hair transplant.  The transplant also can help hide the scar of
the procedure that could be otherwise seen in front.  In order to make the transition at the
hairline more realistic and natural, single hair grafts are used. 

If you have a forehead reduction with hair transplants, the edges can be made with fine hairs. See photos