Does anyone know if it’s possible to modify districts so that they add stability to other districts more than 1 tile away from them? Or for that matter affect districts at all while being 1 or more tiles away? Furthermore, is it possible to make infrastructures change the range of a district’s exploitable range (for example, making farmers quarters exploit 1 or 2 tiles further than usual)? Lastly, does anyone know if there are ways to make walls cover not the whole city, but only a set number of districts radial from a city center or fort? (Please forgive formatting, I’m writing this on mobile.)

I think its possible to change exploitation range of the district by changing their exploitation rule definition, but I'm not sure every feedback will follow it (I'm especially looking at the placement preview feedback here). Infrastructure should not be able to modify this though.

And for adding stability sadly a district only has its neighbours district (district directly adjacent) its borough district("block" of districts) and its settlement districts (all of the districts), it can't really target other district based on distance.

For the wall the fortification rule are not descriptor based but are kinda hardcoded so I don't think you can change them.

I was afraid of that. It looks like I’ll have to settle for increasing farm exploitation range for now and hope further mod options come down the line.