This would only make sense to me if the mystagogue had earned the virtue (temporary or otherwise) from the mystery he is promoting. A mystery virtue is a pact with some mystical power, and having the virtue is rather irrelevant if originates from another source than this mystery. Yes, I am probably on edge with RAW on this, but I like to believe that it is just down to a simplification in the wording.
I don't know if there are any temporary mysteries, to which the original question could still apply in my interpretation.
I'm on the edge about this. I do know that I wouldn't have a situation like Itzhak describes, with an initiation that leads to a temporary virtue that will disappear when the mystagogue loses it. There's just too much work in following an initiation, not to mention ordeals, etc. It would be a it works or it doesn't kind of situation with me as the GM. I would probably base my decision on how temporary the virtue is and whether it seems to be a gimmick to meet the temporary requirements. For example, a mystagogue who used an item of virtue enriched by lowering his Parma for the duration of the initiation, I simply would overrule this. A mystagogue who got the same item of virtue, enriched it, and worked it into his Talisman in order to let it perpetually affect him, I would count as having the permanent virtue.Because even if, in theory, he could lose the virtue one day if he changed Talisman, it's not exactly temporary either. I'm not sure about items of virtues that come with an expiring duration like some enriched plants - although I think that's a situation that's unlikely to come up, given how reluctant a magi should be to build an expiring component into a talisman. The same logic would apply to say, faerie or spirit-granted virtues. I wouldn't allow an easy initiation on the basis of a virtue granted for a month, but I would probably allow it if the virtue had an undefined duration that doesn't expire unless a character breaks an oath, etc.
I'm trying to understand the conundrum here- consider the following:
you have a temporary virtue, you want to initiate it (perhaps for someone else), you develop a script to initiate- by the time you develop the script you likely don't have the temporary virtue
you have a script for a virtue you do not have- is it easier to get a temporary virtue to try and initiate it, or find where the script came from and someone who can initiate it for you.
You have an entity that can grant a temporary virtue. Generally there will be some way to make this functionally permanent (expenditure of might, vis, summoning a daimon) that does not involve an initiation...
ultimately it seems to me that nobody knows if you can initiate a temporary virtue because there are easier methods than trying to initiate a temporary virtue.
I don't think you can. See Hedge Magic p92 in the box "Succurro Magicam guidelines"
"No magical effects resulting from a granted Virtue last longer than the duration of the
charm, amulet, or charta. The mundane results of using the granted Virtue do remain,
however. For example, if the granted Virtue allows the creation of enchanted items,
those items lose their enchantment when the charm granting the Virtue expires."
Therefore, if you can't create a magic item and have it persist once the temporary virtue goes, it's probable that any temporary virtue granted by Learned Magicians would disappear once their spell did.
The Gruagachan chapter isn't so explicit, but then again Gruagachan can't cast blessings on themselves, so you would need a Gruagachan to create the spell, cast it on another Gruagachan, then have that Gruagachan develop a script and teach it while not breaking the geas (as all blessing spells need a geas or limit duration), and then hope your troupe doesn't turn around and say no.
The question would be more whether you could use having it temporarily to initiate someone else who then initiates you after you lose the virtue.
Which again, it should be easier to simply find someone who has the virtue to initiate you in the first place (or someone with the Gift)
from one perspective all virtues are temporary- just the "until" clause tends to be death...
That's only if you equate "initiating a Virtue" with "creating a magic effect". Someone might object that since a character with an initiated Virtue is perfectly mundane and "natural", initiation produces a "mundane" result. For example, if a Learned Magician grants himself the Virtue Good Teacher for a season of teaching, the extra 5xp should not disappear when he stops being a Good Teacher as far as I can tell.
Similarly, you can imagine someone uses Diablerie to grant himself the False Gift, and then convinces some magus to teach him Hermetic Magic and get him into the Order. Eventually, this diabolist trains a Gifted apprentice, and is thereafter found out and stripped of his False Gift (or maybe simply repents and loses it). I do not think the apprentice would lose all his training at that time.
No, but very possibly, the arts are opened as False Powers. Even the Gift might be tainted. After all, opening the arts is quite radical transition, which is here directed under infernal influence, to some extent at least.
There seems to be quite a lot of leeway for the story weavers on this point, and I would not expect the outcome to be the same in every instance.