ANSWER: The VH-Kit will let you convert your VH-55 RO single motorcycle carrier to a VH-55 DM RO double motorcycle carrier. The kit includes 1 additional rail, 1 wheel stop, and a longer main tube. You will use your current ramp and ramp tabs to mount to the carrier and the rear tie down tubes from current carrier will be placed on the additional rail. You will only have room for 1 set of tie down tubes per rail.
If you want to only haul 1 bike then you can disassemble the carrier and go back to your current carrier.