Much of this information is available on the Playstudio / myVEGAS Support page. I thought a few things were worth highlighting, though.

You can now cancel a room reservation and get your LPs refunded.  “If you booked a show, room, or attraction reward online at Mlife.com and find that you need to cancel your reward for a refund, please  log back into Mlife.com to cancel your reservation and have your Loyalty Points refunded back to your rewards account.”

Details have been added about combining room reservations and show tickets.
“For a $5-15 fee you can call the MGM reward redemption line (855.881.6074) and alter your booking reservation — for example, if you and another player are traveling together and each redeeming a room night reward and would like to merge your reservation to avoid switching rooms and/or checking in and out between nights.

There is no fee to visit the box office in person and request that your party be rebooked in adjacent seats for a previously booked show reservation. Requests are honored based on availability.”

Info on the restocking of Rewards.
“We typically update our rewards selection daily by 12pm PST.
We have a limited supply of each reward based on the availability of our partners and our reward inventory is subject to change without notice. Rewards are removed or shown as sold out based on availability. If you purchase a reward that is limited to “1 per player” you will be unable to purchase that same reward until our current offer for that reward is retired. ”

Info on  being able to purchase  a Reward that is “limited to 1 per player” multiple times.
“…   you can purchase this reward once during each offer period. Most rewards’ virtual inventory is ‘restocked’ within 6-12 months. If you attempt to purchase a reward that you have purchased in the past and you get “Error code 0,” it means that we are still on the same batch of inventory for this reward. “