I know what you mean; it's tempting to try and come up with one
simple system to cover all of the permissions cases.
Unfortunately, any linear progression like hostile...ally is not going
to allow some things to be expressed correctly (I don't trust him at
all, but he's going to give me 10 stone this turn; etc.).
Furthermore, I see an advantage in ADMIT that you don't get with
a more general DECLARE: the permission is stated in terms of
structures you own, regardless of what characters control them.
Say I have:
Castle Skrenta  HMS Pinafore 
With ADMIT, my player entity gives all of the admit orders:
ADMIT 1 you
ADMIT 2 all.
Individual units don't issue ADMIT; they're global to the faction.
With DECLARE, Osswid and Feasel would have to issue their own orders.
Furthermore, if they switched place during the turn, they would have
to re-adjust their declarations.
-- Rich Skrenta <email@example.com>