Adding a specialisation in play is always a little questionable, but I think I'd be okay with it in this case if other people are - Muto is pretty much the obvious thing for Fray to have specialised in anyway.
You can get a bit better penetration than that - the formula's (Penetration Score + Penetration Spell Mastery) x (1 + Arcane connection bonus + Sympathetic Connection Bonus). So in this case that would be (2 + 0) x (1 + 3) = 8 as base, and you can trivially include Alcimus' name as a +1 sympathetic connection to get +10. (Other sympathetic connections are possible, but more work).
A couple of suggested additions for the "Familiar Traits" system in the house rules:
Major Positive Trait: Non-Hermetic Power. The Familiar has a Ritual Power that enables it to do something not usually achievable by Hermetic Magic (such as grant virtues). This trait must be taken once for each relevant Ritual Power. Note that this Trait is not required for Ritual Powers that could be duplicated by Hermetic Magic (such as permanent healing).
Minor(?) Negative Trait: Vis requirement. Whether due to a Hunger for (Form) Magic, a deal made as part of the familiar agreeing to be bound, or for some other reason, the Familiar must be provided with at least one pawn of vis per season.
A big part of it is that I don't really like familiars designed with the ability to Grant useful virtues to their maga, which by the Rules is legal. Having it as a major familiar trait doesn't completely prevent people from doing this, but it means it comes with a significant opportunity cost.
I made it a more general restriction on the basis that there were other similar things (like Grant Puissance in (Ability)) that were also covered by it, but this does suffer from the problem that there are other things that would get caught up in it that aren't actually that special.
I don't think it catches any of the active players' familiars, although it will affect Tasia's familiar Vrahos.
Tasia and Vrahos are pretty much a textbook case of stretching the balancing intent of the rules to breaking point--and I'm not sure how much you can do to stop a player determined to accomplish that goal. (I have, though, shot down one or two particularly abusive character concepts before they saw the light of day.) Anyway, I figured your argument was something like that, and I don't object to it, though, yes, it would have no real impact at the moment: I had no intention of trying to persuade another player to take over Tasia.
Given we're probably going to be recruiting shortly(ish), I was thinking it was better to have such a rule in place before someone else wanted to build another such familiar, assuming no-one has any major objections - Vrahos is by no means the only such case I've seen.
An issue I see often for familiars is how they are min/max’ed for the Magus character. It’s not just about granting virtues (although excellent point which demonstrates this wider point), it’s that the creature seems to exist to be a familiar and not a magical animal. As a design principal my personal taste is to see familiars who are creature first.
I’ve broken this design goal many times, which is why I’m now of this opinion.
On player recruitment - keen for more players, just not keen on a few specific players if you follow me. I’ll raise a hand in a private message if something comes up on this point.
So, are we advancing? If so, for how many seasons?
Also, how does the xp work? Gregorius has effectively had 3 adventures in the same season:
Exploring the regio
Looking for Tasia
Horsehunting
He's already had 6xp for the Regio exploration (before we realised we were doing something else in that season too).
On a separate point - is it easy to split threads, or do you have to move every post manually? It feels like the horsehunting could do with being its own thread (not least because it would make our initial discussions on what to do in the next few seasons a lot easier to find, rather than being buried around page 20 of 35.