I am wondering after the Great Elixir transformation as a Magical Being can a magi use the Parma Magica as before the trasformation? Can the mage add the Magic Might and the Parma Magicax5 as a total Magic Resistance? I can not see any block, but I am eager to see other bits of the situation. Any opinion?
There is already ArM5 p.105:
The familiar uses the better of its Magic Resistance or the magus’s Form resistance to resist spells, but this resistance does not stack with a Parma Magica. The magus may choose to use the familiar’s Magic Resistance, but this does not stack with a Parma Magica.
In ArM5 core a magus does not have Might himself.
This is resolved in TMRE p.133 Immortal Magi:
A being with a Might score is subject to Warding spells, including Aegis of the Hearth, and may choose to resist spells with their Might Score or with (Form + [5xParma Magica]), but the effects do not combine.
Worth pointing out that even if his MR from Might is better, he'll want to keep using his Parma anyway if he's going to interact with other magi, unless there's a way to pick up the "Unaffected by The Gift" quality and I missed it.
This is true.
TMRE p.133 - as quoted above - has: "may choose to resist spells with their Might Score or with (Form + [5xParma Magica]), but the effects do not combine". So making this choice after having performed the Parma Magica rítual is possible.
Oh for sure- by "keep using his Parma" I merely meant "keep performing the ritual every morning and evening".
You're quite right, he can use it for Magic Resistance or not as he pleases, but he should keep it running for the social benefits.
Actually, if his resistance from Might and Parma are in a similar ballpark, you could get some really nice benefits from some of the usually-kinda-questionable Folds (HoH:TL 31-32). Combining a giant Parma Ablativa against the first couple spells with Might resistance as an immediately-available fallback that doesn't require two minutes to re-raise is quite nice (but Ablativa is fairly useful regardless). I'd rather take the opportunity to use a fold I've never seen used by anyone and go for Parma Custodia against physical and Might resistance against magical assault.