you need to post pics...but yes you can replace the front....the hairline contour is really dependent on how much side/temple recession you have...you don't want a hair line that is unnaturally long....what i mean by that is if your hair line is going to be lets say 9 inches from side to side because your side hair has recessed quite a bit it'll look off....something like that needs either built in recession in the hairline or temple flaps...
sure quite a few feel "why would i want a recessed hair line if i'm replacing my hair?"
and i always say because you want it to look natural....

hopefully this illustrates what mean...the wide hair line has to stretch an unnatural distance and it just doesnt coincide with the sides....sides dont recede without the hair line doing so as well...the second looks much more natural....sides have recessed so the hair line matches...

of course this is my opinion of what looks natural and others might think that what i have theorized is not true.....