I have always been open in my own applyfic(s)/collaborative work that things might be subject to change. I feel like it helps to give that kind of transparency; it makes it so that people know what to expect. And I have changed some things to make sense with my plot and worldbuilding without discussing. Like, if it's about things that are really central to the character, I would talk about it to the creator, but with more minor things, I tend to just... do it.
For example, I believe your character sheet said that Mele belonged to the people of the land, but with the heritage you described, there was basically no way that she wouldn’t be a hybrid. And since that also fitted with the rest of the description you gave, I just made that call. But with that kind of thing, I'm always very open for people to tell me when I made a change that doesn't make sense to them, and to collaborate on finding a solution. You can never quite tell where the line is without communication, because that's different for everyone and every character.
In this spirit, I have basically decided not to worry about it. My door is open for any complaint someone might have about the alterations. If it's really big, I'll try to contact the person, but if I don't get a response, I just... go with my idea, and if the person involved doesn't like that, my door is still open. And of course I still worry about 'can I make this change?' and 'won't they be upset that I killed their character off in the new version' etc, but I won't let it stop me from making the things that I want to make. The responsibilty to communicate is not all on you as long as you are transparent, willing to listen, and provide a means to contact you, I think. We're adults, we can talk about things, y'know
I can go on and on and on about this, idk, I just really feel this a lot. And well I'm just glad that I'm not the only one I guess lol