I started looking into a larger jig or main sail to increase the speeds in light airs, and in moderate, but if changing sails can cause abnormal behavior ?????
There's nothing abnormal about it, you put on bigger sails, the boat is going to be more prone to capsizing. Hulls sucking down into the water...I don't really know what that means, but the boat would be more prone to capsizing and pitchpoling.
Honestly, it's a Getaway...it will always be a Getaway, so no matter what you do, you're not going to turn it into an F18. Any modification to the sailplan is only likely to make a marginal change in performance. Maybe put a spinnaker on it, but a larger main and jib is probably a waste of money.