I haven't said anything about uninstalling.
Just reinstall Hawaii 2 on top of the existing one, it doesn't create any problems. If an uninstall was required, I would specifically said so and, if an uninstall could create problems, I would suggest a different solution.
If you are worried about registration, as long you don't reinstall Windows from scratch, there's no way you can lose your registration, you can even reinstall the whole FSX, it won't matter to the registration.
In any case, just to be sure, were you trying ParkMe at Kona perhaps ? It's just not there, the only airport supported by ParkMe it's Kahului.