I just did a retag request question and noticed that I had to put one of the mandatory tags up, but retag-request wasn't on the allowed list. I think this should be added.
I'd have to agree with this. Since it's a fairly common request to be made, and it doesn't really neatly fall in the other categories, it should absolutely be added.
Just use support - it makes the most sense (to me at least; past history indicates that a slim majority of others feel the same way).