SPOILER........
There is also Gerard Stiles (another good to evil character) due to possession by Judah Zachery.
I might question this one, VAM. Â Gerard Stiles wasn't exactly what you'd call a "good" or "nice" man even before he became possessed by Judah Zachary. Remember, he also used an alias and was involved in pirating! Â The "Nancy Barrett" character in that storyline charitably referred to him as a "hustler" or some such (I know that wasn't the term used, but something like that) but claimed he wasn't evil. Â Even that characterization of him is somewhat questionable, though, IMO.
My vote for one of the most dramatically changed (and least believably changed) characters is the servant Beth in 1897. Â Her switch from sympathetic, caring maid to handmaiden of the dastardly Count Petofi was hard to swallow. Â I suspect it had less to do with her intrinsic character and more to do with the decision to extend the 1987 storyline (too much so, IMO).

Great topic, Cassandra! Â I, too, am glad that
some of the characters changed for the better (such as Mrs. Johnson and Carolyn), as you mention.
And even that a good, pure, innocent character, Rachel Drummond, remained true to her character (a very Dickensian character, much criticized on this forum, but that's another story ... though I'll just mention that I think it was KLS's most successful character other than Maggie).