As long as your diamond wires are in place, you do not need to worry about over-bending the mast.

Your main sheet will induce far more bend than what your downhaul can induce.

In the attached photo, I pulled downward on the top end of this 31' mast so hard that the front of the boat lifted from the trailer. <img src="http://www.catsailor.com/forums/images/graemlins/blush.gif" alt="" />

GARY