My current character is built upon the concept of make a kind of homo superior with the magical focus going with it. A first step would be to try to improve imself by developping Cr/Co and Cr/Me spells that improve body and mind.
However, when that is done, a further step would be to make those spell really improving his body and mind to the limits of a human being but in a way that once the spell/ritual is casted, it would really change himself and that there would not be any magical effect acting on him. That would be his hermetic breakthough and I would assume that would be a major one.
My main question is: is that something even possible for a player ? I will talk about it with my GM. But would it be something that you could consider achievable in a Magus life ?
Well, there are already high level ritual spells which add to your physical and mental attributes. Those are not ongoing magical effects, but they do give Warping because of the high power of the spell. So your magus does not need a breakthrough to invent them and, in theory, raise all his attributes to +5. He will accumulate some Warping for that.
If you are just making yourself more perfect, you might be able to do everything you want to do with similar Creo ritual spells.
But if you want to make more extreme changes in your body, making it go beyond why humans are capable of, then we are talking Muto, and you need a breakthrough to make the spells permanent or not cause Warping as a long-lasting effect. Your barrier will be the Law of Essential Nature; as a mortal man, trying to permanently make yourself capable of things mortal men cannot do (Str +10, Unaging) is bound by your Essential Nature.
You should check out the Cult of Heroes stuff in Houses of Hermes: True Lineages. That's a mythic and medieval version of what you're trying to do.
And to complete Doctorcomics reply, the rituals he mentionned (Strength/Dexterity/Stamina/Quickness/etc... of the Followers/Heroes, p103, HoH:True Lineages) are rituals with a duration of Momentary: once the characteristic is improved, it is done and cannot be dispel by Unravelling or any other PeVi.
Because they are rituals of level 35 or 60, the mage will get some serious warping, but there will be no constant effect.
Do you have a citation? Newish to the system and currently digging into the rules and committing them more to memory.
I'd say, if your character wants to be truly superior the question might be about inheritance or going beyond +5 to +6 etc. And going to that level of superhuman Characteristic definitely breaks the law of essential nature. Maybe the Law of Divine, since men, created in, His image, etc. It might also require Muto, since he is no longer becoming a perfect human but something else instead.
Page 168, Ars Magica. Look under "Powerful Mystic Effects". "Anyone subjected to a powerful mystic effect gains a Warping point, unless they themselves were responsible for the effect, or it was specifically and carefully designed to work on them.". Because the Stat gain spells are instant, they don't count as a Constant Mystic Effect. But even the lowest level stat gain spell is level 35, and so a "Powerful Mystic Effect". So, no Warping if you know and cast the spell on yourself or a friend who you had in mind while creating the spell, but you would get Warping if someone cast from a Tablet, or as part of a Mystery Cult. Hope that helps!
Something that resonates with this theme is also Fertility Magic (from Ancient Magic, p.54). This can be rediscovered and incorporated into Hermetic Magic -- a quest that would be a great source of stories for a magus interested in this sort of stuff. Although it would only work on people yet-unborn, by acting during their mother's pregnancy, it could give them a wide range of Virtues -- including the Gift!
I'd just like to gently flag that inheritance doesn't work the same way in Mythic Europe as in our world. The son of the blacksmith is big because his dad is big, not because of genetics but because of weird Lamarckian stuff. See also House Trmere's cadre of amber-eyed consortis, who have all inherited the sigil of a wizard who cast a ritual on their ancestors. It -might- be far easier than we think: the physical effects of spells might be directly heritable.
Actually Lamarkian genetics would be more scientifically advanced... I suspect the inheritance rules of mythic Europe have more to do with the aristotilian idea that seen are homonculai and infusion of essential natures than anything as pedestrian as Lamarkian genetics... which may be one of those things that ancient or non-hermetic magic found easy but the Orders theories accidently shut the door on barring a hermetic breakthrough... or it could be considerably easier...