Good luck on the quest to make the Poser horse look like a horse! I had a go at making the horse lower its head, and lift its head, but only using morphs not reworking the entire geometry. Unfortunately, the fixes for lowering the head don't work in the opposite direction to fix things when raising the head, so your method might well be the best. I never got very far on it anyway.

This one was my effort- original and morphed in the same pose for comparison. As far as getting it's head down, it looks better but it's actually made it further from the ground, not closer! If you'd like those morphs to include in your own work, let me know I'd be happy to send them, but I don't consider them finished and they might not be terribly useful if you've regrouped the neck anyway.

So, all the best, because the poor beast badly needs the help.