Currently, districts seem to be controlled by the terrain generation and the only way to change a district is to reroll the city until you get one that both looks the part as a city and also has the correct number and layout of districts you want. In order for districts to be useful for me, especially since my main use case is cities with estimated populations that seem to be at the high end of what this tool is capable of (big enough to have estimated populations > ~50k, I'd have to generate the same city dozens of times in the hope it doesn't, for example, make one huge district and several tiny ones or have district boundaries that would make zero sense if the city actually existed.

A nice way to sidestep requiring you to have spend countless hours on improving a feature that may well be good enough for plenty of other users, the simplest solution seems to be exposing either generation options or allowing the user to edit the boundaries post-generation the way that the buildings within districts can be rerolled. Though, if my assumption on how this works is wrong and it wouldn't be any less effort, I'd love to hear your thoughts on it regardless.