Exalts, charms of different splats, E2
Generally, Exalts getting non-native charms half-heartedly discouraged in E2. Like, you weren't supposed to do that, but every single celestial splat had an official White Wolf/Onyx Path-approved way to say "No u, limits are for other people" and get access to something they weren't really meant to get access to.
Typically, thanks to a Glories of the Most Hight late E2 charms.
Solars had ability to purchase Abyssal and Infernal charms if they had a special charm (because
of course), Abyssals had Solar Mirror charms, Infernals had potential to unlock a bunch of additional charmset by talking with a bunch of Yozi that didn't opt in into Reclamation initially, Lunars had abilities to steal Raksha charms/stuff and buy divine charms... Etcetera. Broadly, if Solaroid really wanted, they could break stuff. If their storyteller approved, ofc.
Waaaay back, Twilight anima also allowed to get non-native charms really easily, but that was nerfed into the ground because it made Twilight into absolute gods on the earth.
Aside from ways that didn't fuck an Exalt over, there is always going Akuma, but it is generally always bad idea to go Akuma.
Dark pacts/Infernal Investiture mechanics allow purchasing non-native stuff, but if you aren't cheesing it with Soul-Rending Practice, then it is going to fuck you over. There is also some talk about Werewolf gifts being learnable by in-universe logic, here and there, much like Paths, but it isn't super-common topic of discussion.
DP once mentioned possible access to non-splat charms if we could talk relevant Powers into "unlocking" their charmsets for us. Rando comment in a early game of the quest about mechanics that are still definitively up in the air isn't very binding, tho. This isn't set in stone or anything.
I'm kind of doubtful that we'll actually crush Mab that badly.
We didn't actually invest into anything that would enable that sort of ridiculous sux, so there is no need to doubt; there is absolutely no chance whatsoever for that sort of stuff to happen.