Kilo: It is possible that HTC accepted an LA5F skin on an LA-5FN because they have no interest in adding the -5F model and the 2 are similar. Sometimes you find crossover where HTC allows certain leeway with skins and what planes they belonged to. It really depends.
I have not done any Lavochkin skins myself, so I can't say for sure. I would suggest that Greebo is the guy to ask, since he's done all the LA-5 skins we have so far. He would know best which of his skins were La-5F and which were La-5FN, and whether HTC allows that kind of crossover.