The issue for a UH-1N is not really the tail rotor. The tail rotor side switch is easy. An N model has a totally different nose (more pointy and thinner chin windows) and a different engine cowl/sail area with dual intakes for the dual engines. It can be done, but takes a lot of work, not just some modifications.
You can see the differences below.
UH-1H
UH-1N
Your better bet is to get the Panda or Dragon (same plastic in the boxes) UH-1N in 1/35.