For redeeming marks for honor, just Shift click on the Mark you have, then choose a number.

same goes for when you want to downgrade Badges.

An example, You have 90 Marks of Arathi Basin. Go to the honor guy in Dal, Shift click on the arathi basin mark, insert (and here is where my mind fails me) either 10 or 90 marks in the pop up screen.

Boom, 10 or 90 marks turned into Honor.

Hope this helps my friend.

Stephen