Ugh...I need some advice.
I've been playing as a female Miqote since I started so all the story I've done is as her. I kinda want to swap to Male Viera after playing around in the benchmark I found a look I really like. The issue is my characters name is definitely not fitting for that appearance. I'm not opposed to buying a name change but I've got so much glamour tuned for female Miqote that I'm not sure how to adjust. Maybe I just don't? Plus there will be this weird feeling of it being a different character playing through Endwalker that I'm not sure I want to do it. I have 3 Fantasia so I can swap back if I really hate it I guess but I don't know.
How long have you been playing as your current character? Admittedly I'm probably not the best person to answer this, as the most I've been willing to do with a fantasia in the past was make my character a few inches taller lol, and don't see myself changing anything else beyond that. But all the same, it seems pretty natural to have some mixed feelings about changing the look of your character significantly (unless of course your original character doesn't resonate with you at all anymore), especially if you've playing with that character for a while. I think the glamour issue can be tough, since a lot of items are still unfortunately gender locked, and even for those that aren't, they may not fit the style you're going for with a new character. So that's definitely a good thing to keep in mind with how important all that is for you as well.
I think if it feels weird to play as a different looking character with main story content in Endwalker, perhaps one thing to consider would be playing as your current character until you finish the 6.0 MSQ, and then that way you maintain that continuity of playing the MSQ as the same character, before deciding to maybe switch to something different during the post-6.0 patch cycle. Of course that depends how badly you want to play as a male Viera, and if you want to hold off on using Fantasias for now.
If you do decide to Fantasia, I would consider giving it maybe a week or 2 before deciding if you want to switch back or not, as I imagine it may take a bit of time to get used to and adjust to a different looking character after all this time.
Apologies if that wasn't very helpful, but just wanted to suggest some things to consider as you're deciding.