You can always shorten it without traditionally pulling it. You can scissor it, if you are careful. When I pulled manes for the last show barn I worked at, I always had to do several every week, and we had quite a few with very thin manes that could not be pulled, or they would have none left. The technique we used was to comb and then back-comb as if you were going to pull, but then the hairs you would normally pull out, you would just trim the length you wanted the mane to end up. So when you comb the shorter hairs back down, it doesn't look choppy. It takes a little longer than traditionally pulling, as you don't want to do too much hair at one time, but it's very effective, especially if you use thinning shears when you do it. So instead of comb up, pull, comb down, you would comb up, trim, comb down, and repeat. It does take a little practice, but the end result is worth it, if there isn't a lot of mane to sacrifice.
"Keep a leg on each side and your mind in the middle"