I'm not sure if this actually works as I have not tried this myself.The player name appears to be bound inside the .fhp file so renaming them doesn't really work, at least for me.
Yet, what you could do is change your username and then rename the .fhp files that you've exported into FeralHeart>presets and see if it'll be applied to the characters. I don't think it'll work but I could be wrong.
What I would do is try this, but if it doesn't work- delete the .fhp files you renamed and reexport your presets to renew them for usage.