Rear Re-Gearing?

The problem is, You can't change the gears in the rear differential without changing the gears in the transmission (aka: transaxle) also. Because, you can't have two different gear ratio's running at the same time without braking drive line parts. (exception would be for racing purposes, usually in the mud or snow).

Motive Gear is a really good gear set. I have been using them for years.

It would be a pain in the ass. BUT, It can be done.
It is a lot of work and you would have to make sure that you can get a set gears to match the rear set.