Can a magical creature avoid acclimation by having an enchanted item affect them, possibly even constantly if it's a buff item? I'm looking into the idea of a Great Beast that retains its talisman as a way to avoid losing its Might (though I'm not sure how much of the original magus is retained once transformed...).
Yes.
By RoP:M p.53f Acclimation Effects: "Magic characters can also protect themselves against Acclimation by being the targets of powerful Magic effects that do not originate from a creature with Might, <...>". Looking up the table on p.54, even a low level effect would suffice for that, if applied constantly.
I don't see why not (ref: provided by @OneShot above). It would probably need to penetrate though.
But a Talisman with a nice booster effect? Go for it!