I have a query that a reading of the books i have doesn't solve.
As a sinister necromancer my character likes to travel around on a re-animated skeleton of a horse. This has been enchanted as an item. It can also fly. It is very cool.
But i'd like for this skeleton horse to have a personality of a particularly bad tempered (except to his creator) living horse.
How would i go about this?
It doesn't have to be a thinking creature, just act like one.
Stick a spirit into the bones 
You are trying to give him a defined animal personality. As such, I think InAn should serve your purposes. The personality you are describing is readily observable in mythic europe: warhorses behave like that. Go ahead and do it. it is certainly a cool item 
Ever thought about challenging Hunger for his starring role in the apocalypse?
Xavi
Actually, it is ReAn to control the bones to act in a certain way with an In component to differentiate the caster from the others.
Binding spirit is another way with caster exception.
If your lab has a Warping Score (see Covenants), it has the chance of infusing any spells or enchantments you invent in the lab with a Personality Trait. However, it seems that you have already made the item, so this might not be a solution.
I would use MuAn - you are altering the corpse of a horse to express a personality, which is something it cannot normally possess because it is dead. I'd look at the MuMe guidelines for a suitable base level.
Mark
If dead horses don't have personalities there is nothing present to change and he has to use Creo.
However the spirit would be cool 