Yes, YOM = year of manufacture
You're close. Here's my experience:
1. Buy the SET of plates. Must be correct year, both front and back, and legible. No exceptions.
2. Take them to your county tax office. Mine made a photocopy of the plates, and confirmed they were color correct for that year, legible, and that the numbers/letters were not in use.
3. Pay the registration, ~$10/year. It has fixed, not rolling, expiration- all YOM plates in TX expire in 2013. At that time, all YOM plate users will go to the tax office and re-register their plates for another 5 year period.
4. Tax office gives you a 3"x2" metal tag with the expiration date. This must be attached to the plate (I used rear).
5. No annual inspection or registration. You won't have any windshield stickers!

6. If you sell the vehicle before the tag expires, bring it down to the tax office and you'll get a prorated reimbursement for the months/years you didn't use.
Others might have a different experience.
The only hiccup I had was when one clerk didn't want to allow me to run Farm Truck tags since my truck isn't for agricultural use. The supervisor weighed in and allowed it. (I argued that they allow YOM Dealer Plate use, even though the user isn't a dealer.)
Bill