Late, but, as a big enjoyer of Self-insert fics, I don't mind they follow the standard isekai format and don't go overboard with changing the world. Sure, some change is good and characters should be alterred due to the space an SI fills, but letting the overarching plot flow is a great boon for fanfic authors.

Fanfic is about enjoying and, forgive the wording, messing around with established lore and setpieces. Kind of like how gaming has the modding community, the literature community has fanfics who choose to spice up or manipulate existing stuff. You don't have to necessarily go on and completely overhaul or make full-on novel tier total conversions if you get what I mean.