Spell alterations and the Far Realm
Most of the 2e books were published before Gates of Firestorm Peak introduced the Far Realm, and there was never any mention of that place in any subsequent Planescape book. So there is no official ruling on how the usual changes to magic from plane to plane would apply to casters, spells and magic items connected to the Far Realm. I have a couple thoughts here, but I'd like to gather ideas from anyone who has them.
For most schools of wizardly magic, I think it's simple enough to say that their spells just all get altered to fit local norms, sort of the way Limbo and the Outlands alter everything cast there, though with much stricter limits on conjurations and other plane-spanning spells. This more or less agrees with the 3e Manual of the Planes, which briefly describes magic limits there.
My bigger worry is clerical magic. How many planes away from their deity's home plane is a cleric in the Far Realm? Can they have any connection to their power there at all? No published book I've seen says anything about this at all, but by the usual Planescape logic, it does seem to make most sense to just cut clerics off completely. Maybe a power key can somehow cut through, but I'm not even sure of that.
Similarly, magic items ought to lose a lot of pluses when taken to the Far Realm. How many? Maybe all of them, regardless of their bonus. It is simply supposed to be as far away from anywhere in the multiverse as any PC is likely to get, so no normal plane's items should maintain their attunement there. (A more complicated question is whether a deity visiting the Far Realm can still use their normal powers there.)
I'd also suggest that chronomancy simply breaks in the Far Realm, since time does not flow there at all.
This all sounds fairly rough on caster PCs especially, but I'm ok with that. It's meant to be a bizarre, alien place where the usual laws are even less applicable than in the chaos of Limbo. It should be an uncomfortable struggle for any PC.
But I'm keen to hear if anyone else has clearer and more interesting ideas than mine.