(source: this forum thread)

Nikolai wrote:
"New SOP Knowledge check: Requesting some info on the Spellkeepers' Final Solution"

You consider the problem from all angles, and this fact is inescapable: the close link between the revenants that the Spellkeepers will become, and the Keep with all its stored magic and knowledge, is simply incompatible with retaining the personalities of the transformed. To put it another way: those that go through the ritual cannot both retain their identities and gain the power that is the object of the exercise. To recap a bit:

However, after close study and consideration of this ritual specifically and similar types of undead (oathbound spirits, various revenants and guardians, etc.) in general, you can be fairly certain that their existence will not be painful or tormented. The people you know will be stripped of their mortal values, goals, desires, and will retain only the will to carry out their protective mission. So long as they watch over the knowledge they were sworn to protect, they will not suffer; their existence will be fulfilled.

What you definitely can do, near-trivially, is alter the spell to allow yourself to be recognized as an ally by the guardian spirits. You won't be able to control them as such, not in the sense of direct unquestioning orders, but they will recognize you as, essentially, part of their mission (so long as that doesn't create conflicts with protecting the Keep, etc.). This, combined with faint echoes of their previous personalities, will ensure that the spirits will treat you as an ally (so long as you don't try to do anything like plunder the Keep or whatever).