Any further mods are probably unnecessary. I have a Yamaha fuel-injected scooter and after installing a Yoshimura pipe, it runs great. I also know someone with a Vespa GTS250ie that added the LeoVince 4Road to his with no further tuning. That said, whether the Kymco will run and idle just right after putting on the exhaust remains to be seen, but I'm willing to bet it will be fine. Since it is water cooled, so long as it runs smoothly, heat buildup due to any slight leaning out of the mixture should be of minimal concern. I don't recommend fooling with the air intake tract on any FI scoot since usually that causes more problems than it solves, IMHO. An exhaust will probably not enhance the scooter's real-world performance that much (if at all) the reason I want to do it is primarily so the bike won't sound like a lawn mower.
If a variator exists for this bike, I'm unaware of it. However, putting different weights in the variator shouldn't be too difficult, since most of them are universal. The bike is a bit lazy at launch, and that could probably be alleviated with weights, but keep in mind that will also have a potentially negative effect on top-end. Messing with the variator is like a game of tug-of-war with low and top-end power.