I don't follow Parelli per say....but that said...doesn't matter, it's all the same basic stuff....and SpiritHorse is right on.
Twisting the lip to make em stop nipping is a way to discourage a horse but it won't work with a horse like Cisco.
If the owner wants to continue to give treats, they can be dropped into a bucket for him in his stall. He can still continue to be hand fed treats as long as he is not allowed to mug people anymore. That is, he is to wait to be invited in for a treat. He's given the treat, then told to back up a few steps immediately and stay there and not creep in toward the person. This is totally possible. I've worked with horses who were treat driven thanks to overly doting owners. And it did work out just fine. The hand treats continued but the horse understood that there were rules and was fine with it.
But if the people are going to be inconsistent in handling him, then it's best he be fed treats out of a bucket or such. Prevention
is the key here. Stop the biting/nipping before it even happens.
One way is to give the horse attention before he asks for it. Nippy/biting horses like Cisco crave attention and get bored and find ways to entertain themselves by being nippy/biting toward people. So, if you invite him in and hug his head and rub his face a lot, that will help.
Also, for the horse to be nippy/biting he's got to be close enough to people. So, he should not be allowed to lead too close or to stand too close to anyone unless invited in. If he steps in too close when you are leading or when you stop and are standing near him, simply twirl the line assertively (not wimpy) at his shoulder or chest and soon as it backs away (it'll take the rest of the horse with it) stop the twirling.
You don't want to twirl constantly...that is, twirl only when needed, to put pressure on the horse to move. You don't want to walk and twirl the line or stand there and twirl constantly even when the horse isn't in your space....because this will desensitize the horse to it and render twirling useless....then you'll find yourself twirling constantly and with more energy.
So, only twirl when needed.
Secondy, how exactly do you invite them to your space? Through body language?
you kiss or cluck and back step to invite them in. Some people will even use a "come here" motion with their hand. Think like....you are inviting a friend into your house, you have a different body stance than if you are blocking that person's way into your house and wanting them to leave. The horse can tell the difference if you are looking inviting or not.
Also what SpiritHorse said about drawing the horse in is on target.
Anyways, thanks to anyone who took the time to read my silly questions!
There's no such thing as a silly question. How else are you supposed to learn if you don't ask?