Hey hey! Gender changes on anything gen 6 and beyond have been a topic I've seen pop up in searches here, often times with the only answers being "yes it's possible but we don't know how, so better make a new savefile". That said, while I have been lucky enough to start with a female character, my best friend was not so lucky, but here I was a few weeks ago and wanted to give it a shot anyway. Aaaand: this was a triumph, I'm making a note here, huge success!
It was somewhat tedious but also exactly the kind of thing I sometimes like to do on a Tuesday night at 2AM, going all Ema-like on it, spending hours staring at hex editors to spot any differences in the save files. What it boils down to is that I ended up transplanting a whole lot of data from my own Pokémon Y save to hers, because there's quite a bit of unidentified data in there, waiting to be reverse engineered. I may have transplanted much more than necessary, but we did get her game up and running and haven't heard about any issues so far.
If you want, you could send me your savefile and I'll have a look. I kinda want more real world save files anyway to hopefully figure out some of these unknown data blocks in the files.
For example, I copied over most of my own trainer data (editing the name wherever applicable), so when it did finally work, we did end up with a character that had the exact same outfit and looks as mine, but we settled on just unlocking all clothing options to get around that limitation. And just to clarify, I have no idea currently whether it was required to do this at all, but I figured if I did, I'd have the biggest chance at succeeding. There's also a bunch of unidentified flags and event constants that may or may not have any impact on things in the overworld but also may or may not have an impact on your character working or not. Lots to figure out, but I did get *one* savefile working at least.
Hey, just wanted to chime in, I still have to do this process for my best friends Moon savefile as well (I did succeed on doing a gender change on her Y savefile, by transplanting a lot more data than was probably necessary from my own file, but at least it worked that way). So while I haven’t gotten to the Moon (pun intended) savefile yet, I’d like to see how far I can get at figuring out a few more things regarding the currently unidentified savedata blocks.