Line To Circle UI Toggle Button

would it be possible to get a ui button that changes the structure build mode from line to circle please

why not? i feel like this would take 10 minutes to code, since the calculations and code for area build already exist.

I don't believe the engine is able to modify json files dynamically while in-game.

But, but... can't you just program: if LineSelected then UseLineFormula, else UseCircleFormula.
Why modify files on the fly?

Circle and line area build are both dictated by a buildings .json file.

That's what I mean. You put both code pieces in that file, and depending on user setting, you call either Line or Circle?
I'm no programmer, but this seems pretty ok to me.

Unfortunately no, it ain't that simple, json files follows some specific format to store data, they don't contain any type of "real" code (barely some basic logic for specific stuff).
Uber would require to make some changes in order to make what the OP suggested (I personally think it would be cool to have such toggle in the uber bar, lines of factories are boring)

Would be great to have it!