Vespasian, thanks for setting up this thread.
I'd rather treat the formulation of Ezzelino from https://forum.atlas-games.com/t/heroes-birthright-duration-and-warping/188/1 here first, though:
"Hermetic magic doesn't know how to change Aegis parameters without a breakthrough -- so it can't be done with metamagic either".
To me this formulation is sharp, concise and convincing, while discussions about "Which spell is Hermetic, and if so, how much?" can also lead one astray.
Cheers