I was very fortunate to have a 'trainer' teach me Level 1 of Parelli. The knowledge that I learned could not have been achieved from a DVD or book. We stretched his 10 lessons to over 1/2 a year, due to weather and other committements. That was to my advantage. It gave me a lot of time for homework.
That said, I will touch litely on horsenality. It's not just about categorizing your horse, its about taking that information further to educate both horse and rider. My horse is a LBE. She craves creativity, imaginative tasks and can't stand to be forced into anything. She hates to be bored. You need to speed things up, be enthusiastic and come up with variety in your lessons.
I was riding her in the roundpen. She hated it, but didn't seem ready for the rest of the world yet. What she really needed was variety. To do groundwork at another location, use obstacles, make games of it, use psychology. And the most important thing I learned was to 'whisper' my commands to my horse. She was terribly bothered if I was direct with my command. She wanted just the slightest of asking. Yes, she is very sensitive.
With every horsenality there comes suggestions for training methods. If I had not had this training, I could easily have thought she just needed a 'firm hand' I could have escalated my training methods, bits, and my expectations. And, should I ever sell this horse, I can share this knowledge with her next home.
Just think what the knowledge of horsenalitys could help you with. When horseshopping, you might be able to ask better questions and notice certain characteristics in the horse that would make for a better fit down the road.
I know, you'll just say I'm a Parelli follower. Actually, I try and take the best from all trainers and mesh them together.
And yes, a horse can have 2 different horsenalities. They can be one most of the time, then lean towards another when taken off the property, to a horse show, etc.