I used to rename my characters only during my very very first plays, when I had first gotten a PSX (which I bought from my friend and which he sold with all of his games, including FF7), before I even had a memory card and before I even knew how to get past the guard scorpion. I named Cloud "Deathlord" and Barret "Sh**head" the first time, and the next time I named them "I am GAY" and "I am GAY 2." (Which made it extremely funny when Barret said, "I am GAY, you set the bomb.")

Other that that, the only time I've ever renamed a character was during my most recent playthough, where I changed "Aeris" to "Aerith," because Square has retconned that to have been her official name, and I did it for continuity's sake. This was when I had just bought DOC, when I was speed-replaying FF7 with Gameshark codes, after which I rewatched AC and then got into DOC. Although it was kind of moot because Aerith's name is never mentioned in AC or DOC.