Hi BN
Wersi created and programmed a special voice bank for the Yamaha styles that matched the Yamaha voices, thus no conversion of style is required.
It can be done manually, but it is not an easy job, particularly as most of the Yamaha Mega voices are played using Midi instruments. (IE; A Mega Guitar is played and programed by using a Midi Guitar, rather than a keyboard etc.)
Hope this clarifies it for you.

Bill