No, Eris is Eris. While she was stripped of most of her light and partially affected by darkness, her corruption wasn't to the degree of Yor. However, when she lost her light, she was no longer a Guardian. Now, we see abilities coming from her that were never used by Hunters. (She was a Hunter incase you were wondering). Her abilities aren't from light, but from darkness.

Dredgen Yor, in his own words, had a "change of perspective". People change, they don't transform into other people.

Physically, no. Mentally, they do.

Point is, Yor is Rezyl, just like Vader is Anakin. Any argument otherwise is semantics.

How can two minds be the same person?

It's one mind, just changed.