The point about the A6M2-N is that apart from the floats the rest of the internal and external 3D shape is almost identical. It would just need the gear deleted and the 3D shapes of the floats made. I could do a new skin for it based on my existing A6M-2 template so there is not much work to do there either. The flight and damage models would need revision, but still much less work than a new aircraft.
Our N1K-2 however was a complete redesign of the N1K-1 land plane, which in turn was based on the N1K-1 float plane. The 3D shape is totally different, mid-wing, long gear and short fuselage on the N1K-1, low wing, short gear and long fuselage on the N1K-2. Animating different gear and flaps on the 3D shape is a big job for HTC. The float plane had a less powerful engine too. Flight and damage models would be substantially different even for the land plane N1K-1. The cockpit art might be transferable though, would have to research that to be sure.
I've already said the Ju-188 wouldn't really work as a variant. The 109T though as it was used operationally was essentially a 109E with longer wings, I can't see it getting modelled as a carrier plane. It would just need an altered 3D shape and a flight model revision.