Yamaha's Clavinova digital piano is a large keyboard that can come with either legs or a stand. There are different ways to get casters onto the keyboard depending on what kind of set-up you're working with.
If you just want to be able to transport your Clavinova while it's on a stand, just purchase casters for your set-up. If your stand is not compatible with casters, it is best to purchase a stand that is compatible or comes with them pre-installed.
If your Clavinova has built in legs and you're crafty enough to be able to do some drilling, you can drill a quarter-inch hole vertically through the legs. You can then take a threaded caster and place the stem through each hole and attach with a washer and screw anchor.
In order to transport your Clavinova easier, attach casters to your case as well. Attach two casters at one end of the case by drilling a quarter-inch hole in the bottom of both corners. Place the stem of the caster through it and secure with nuts and washers. You may want to attach a handle to the other end as well.