No.MJMARSHA said:
The existing paint can be used as a base coat for whatever you are going to use as the top coat.
I would recommend that when ready to paint, degrease the entire rifle, and paint over the existing paint.
FYI, I think I've found a cheaper finish that I once read is Tantal's recommendation to match the factory black. Will be testing out soon, but it looks promising. It's actually an epoxy lacquer auto chassis paint from Eastwood - http://www.eastwoodco.com/ - they shipped it faster than expected, so I need to get my plum kits finished up & coat!
Cheaper than gunkote too