>>>That will eventually wear out the haul loop. Also, the friction impedes the flow of the rope through the haul loop, more a concern when raising the pack than lowering it. I think a better approach is to clip a carabiner through the haul loop and use it as a pulley. This facilitates control both lowering and raising a pack, and confers a 2:1 mechanical advantage when raising(minus some coefficient of friction) a pack. A noticeable difference with a heavier pack.<<<
If you do it that way, then don't you need twice as much rope as the longest pitch you need to lower, plus a little extra for the two knots?
What I would do is bring a biner, 25' of cord, and then use one of my tarp guylines.
Take a tarp guyline and sling a tree or tie it around a rock or whatever you're anchoring to, clip the biner to that, take the 25' rope and tie a loop in the end then girth hitch the haul loop of the pack using that loop, tie the rope to the biner with a munter hitch, then lower away... Maybe tie the end of the 25' section to something for backup in case you misjudge the distance.
Better test different diameter rope with your expected pack weights before hand. I'm not sure how much weight you can handle for a given diameter of cord.
Edit: This method assumes you have trees,sturdy shrubs, or heavy rocks with cracks in between them close to the edge of the cliff that you can use to anchor with.