Um well. OK.
1. in this instance, the character's personalities very much do have to do with their chosen pronouns, this is part of their writing and their characterization. it's not a frivolous character trait. They aren't paper dolls for the player to customize however they like.
and 2. it's extremely weird to expect the ability to change an established, non-customizable character's pronouns at all. This isn't a kingdom or god simulation where you are in charge of everyone, it's a narrative visual novel. And it's especially an odd request for trans and non-binary characters. This would be a horrendous idea to implement and would only encourage transphobia and bad-faith arguing that the character's gender's are "up for interpretation". We live in a world where transphobes demand that trans people change their language and presentation for cis comfort. Because it's "weird" or "hard to understand" and it's just "easier" to use a different term. While I am not saying that YOU'RE asking this because their transness makes you feel discomfort, I do think this is something you should keep in mind next time you get it in your head to request something like this.