Well first for the bridge simple solution. Slacken the strings, remove the back plate and the 2 screws that are connecting the underside of the bridge to the guitar body tighten them so they go in towards the guitar body. Tune back up and sorted. That is what lowers a floating bridge. If still a little high tighten some more. Unless your on about the action being to high then that is a simple fix also. You haven't really considered the pickups too well then cos as soon as you take the pickguard off u will have a cavity that fits a humbucker not a single coil. Either have to fill the cavity and re rout it or have a single coil with the chance of too much movement and vibration if not fitted correctly. Try something simple first before not liking the humbucker on the yamaha, lower the pickup away from the strings, it won't be as powerful and will add extra twang. I quite like the humbucker in the yamaha, I just add some bottom end on an eq pedal and sounds nice.