If you mean adding VST sounds to your keyboard's voices, there are sampling programs that make it easier to sample sounds for all MIDI notes, at different velocities, and you can create a soundfont from the samples, then import the soundfont into the Yamaha Expansion Manager to create a new user voice. I have no knowledge or experience related to any of that, but I believe there are Yamaha "power users" who like to do that sort of thing.