I know making an acc just for this is probably frowned upon, but as a longtime user who is GNC and questioning I feel I should chip in.
First off, I don't like the change as a fan of the character. Obviously not against trans people, but against how this 1) reads for someone assigned female at birth, whose entire shtick was fighting against it, and just having it announced as what they want like it's ok now. It carries a very icky "groomerish" tone to it given how they were raised, and 2) sends a dangerous, oft-repeated message about acceptance where to be feminine as a guy you must be a transgirl. It's just as unhealthy, and takes representation from androgynous men (who are already mistreated for similar reasons in trans communities) and moves it to totally trans people.
My point being not every trans umbrella individual is on-board with this. I'd have much rather any character who wasn't in this situation been used for this honestly. Doesn't help that the game has arcade format storytelling and the dev statements are explicit in stance but unclear in detail (Why is the mars symbol an androgyne symbol now instead of a female or trans symbol? Is the character mtf trans or just genderfluid, which was my impression from the game without interview context? Is it because this has pushback in japan and they want it to go smoothly there?).
TL;DR I think the message of trans acceptance is good, it was just handled clumsily and with the wrong character.
I'm not alone in feeling this way:
https://old.reddit.com/r/Guiltygear/comments/wj1rn8/so_i_noticed_this_symbol_on_bridgetdoes_this_mean/ijh1ycj/
But I realise this isn't the tagging issue, as for that:
By and large I agree with keeping pre-strive bridget as 1boy across the board (because erasing that identity would be just as insulting to crossdressers who are having this happen to their characters more and more), I think most are in agreement with this. As for strive as 1girl, that seems to be the next best thing, though as has been said above, not without issues. Not sure how to deal with NSFW girl posts that show masculine features, or NSFW art with SFW parents. I think splitting strive into 1girl for most posts, and 1boy for NSFW posts is just illogical from a site usage pov.
The problem is that the ideology is that a trans person is their gender regardless of what you see, but obviously that goes against how sites like this operate to begin with, it's completely dissonant and there is no way to reconcile it. That carries unfortunate insensitive implications to real people. In my opinion with a character it's ok because it's in the nature of stories revolving around topics like this and art sites in general, none of these characters are people in other morally unacceptable tags, and shouldn't be looked at as a contradiction of real trans identity just because the site has to work a certain way, it's just how the cookie crumbles when it comes to body judgement. Maybe a disclaimer explaining all these tagging difficulties for this character, no matter what decision is made?
Like others have said, it works for a spoiler or reveal trope character whose whole point is they are known for their chosen gender and treated that way in-universe from the get go. Bridget has 20+ years of being an otoko no ko under his belt (this goes back to what I said about their taking representation away from one group and handing it to another, this happens), and seeing the art even post-coming out, that attitude isn't going away any time soon, and all sites like this will suffer for it.
Overall I hate this headache of a change because I need to make huge disclaimers and explanations about how I feel about him being a she now, and listing all the trans dressup and skincare guides I follow just to not look like a bigot. Sucks but what can you do, it's an important discussion to have because more and more characters like this are going to exist in the future, and public opinions will march with medical ones, so best to have a stance right now that keeps things smooth.