I count three reasons it's impossible and three reasons why you shouldn't even if you could.
1. The sword is connected to the Rider.
2. The sword would have to pass through the body of the Rider to reach the part of it that connects to Mathilde's soul.
3. The Rider does not have a level of intelligence that makes it capable of learning a sword style.
1. If the Apparition gets loose after being taught that technique it would be a horrific menace to the Wizards of the Old World.
2. If the Apparition gets loose and then gets caught by someone else, they could reverse-engineer the sword style from it.
3. The Apparition's less-skilful application of the sword style would mean much more people would be able to survive it and work on figuring out a counter to it.
1.2. Part of the binding process is customization, make the part of the rider connected to Mathilde's soul the hand. The Dämmerlichtreiter is Van Hals metaphorical right hand, the apparition is Mathilde's metaphorical hand, it is cast using Mathilde's right hand. + Ranald coin
3. Using Mathilde's knowledge the same way Wolf does. Is there at least one magister with some fine apparition control, like bite here, use paw like this? It's called an ornerier familiar and familiars can do this, and Mathilde has the control. Use that and expand + Dämmerlichtreiter + coin + crit.
1. ^ Work with it to use Mathilde's knowledge. The things this would be used on are possibly greater threats. Any wizard facing this in melee is already fucked.
2. ^^ The same could be said for all of our other creations, ROW could let the chaos hordes pour south much easier, MAP could lead to unprecedented control over enemy armies, MMM could do all sorts of insidious shit.
3. If the enemies of the empire have to spend time learning to counter Mathilde instead of one of the million other threats, that is a bigger victory than any spellcraft.
This goes from an esoteric technique that a single mage and a few dwarfs can use to a terror on every battlefield the grey order enters. I'd take that any day. We lose the element of surprise for a single technique in exchange for sooooooo many positive tradeoffs. Every orc, goblin, fimir, chaos whatever isn't going to get that training, and if they do it will currently only negatively affect Mathilde's ability to personally beat them in a sword fight. Forcing the enemy to learn a skill with literally no other applications instead of one that would allow them to better fight literally only Mathilde as opposed to any and everyone else is a Huge Win. Not using knowledge is the same as not having it (Pretend that was a quote from someone universally liked.) We have used the sword about a dozen times, this spell would have it used by people who fight a dozen battles a week!
Not doing this if we can is redonkulous!
Future application of a partial summoning of only the sword from Mathilde's hand? Or another in the order from a mastery?
Edit: I meant to put this somewhere, but couldn't find a place: Fear and respect useful for anyone, weaponizable for Mathilde, possibly more useful than the actual technique in any not murder situation.
Tldr: I think giving the apparition guard bypass is possible unless its a game balance thing (would understand, though it would make me cry one gangster tear at the loss of cool potential). Giving our apparition (my vote is to name it Jerry) and by extension the entire grey order who uses this spell guard bypass:
- People can learn how to counter it more easily and know they might need to.
+ The grey order bypassing the guards of the elite enemies of the empire will force them to have to learn a skill only useful in countering a single swordswoman.
