I think this would be an easy addition that'd make a lot of people happy. I'm more than sure many people (including myself) wish they could edit their characters, whether it be something as small as choosing a different hairstyle, change markings; to bigger things like changing their race or gender entirely. The closest thing we have to doing something like this is deleting the character and starting anew, but most, if not all, have made a lot of progress into their characters and it's just not worth throwing away to simply change their Guardian's appearance. While selecting your character X/A to log in Square/X to delete and then the addition of Triangle/Y to reedit as an example. Why have the same old boring look when you can change things up as simple as that?