I have never gotten around to trying it so I can't vouch for it, but Vampire the Masquerade: Bloodlines computer game has a mod developed for it which allows a considerable amount of corrupting and recruiting of NPCs . Notably the Japanese devil-hunter Yukie in this clip at 0:55, turned into a Nosferatu.
Also some do-it-yourself EC is possible in Baldur's Gate, particularly BG2. Using the Girdle of Masculinity/Femininity,and Helm of Opposite Alignment on a character then casting remove curse on them to remove the items will leave them with their original sex but opposite alignment, useful if you want to keep a baddie in a high reputation group or a goodie in an evil one.
In BG2 when travelling through the underdark the party members will temporarily be transformed into dark elves, this is permanent for a party member if they happen to be "dead" when the illusion is lifted and they are resurrected afterwards. So you can end up with characters of good alignment turned into evil drow.