the example code here has write support. i havent tried it as i have no writable tags yet, but it compiles fine and works just fine for reading tags at least. it does look like it function-izes all the commands so you dont have to mess with the hex.
as a note: if you sign up with TI you can get free samples of rfid tags, theres only a few that are 13.56mhz but you can get 5 of each of up to 5 products so 25 tags
they have one of the best and most generous and unstingy samples policy, probably to retain some market dominance