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I am playing a primarily lawful good party (Frank the Monk, Minsc, Anomen, Aerie and Nalia) and wanted to include Viconia just for kicks. I summoned the helm of alignment change and have just placed it on Viconia. I am curious if anyone out there knows what effect this will have on party harmony and/or possible romances.

Since Viconia is now Neutral Good, she should no longer complain when the party's Reputation becomes high. But her voice set, romance dialogues, party banters, other scripted speeches, and general personality will still be exactly the same.

I once thought up a MOD that would include the Helm of Opposite Alignment, but blanched at the prospect of writing a diametrically-opposed personality for every single NPC in the game that could ever be capable of wearing a Helmet.