It should theoretically be possible. The AsteroidFieldMiningBaseModules.xml file in the Dark Avatar Data folder had a nice comment listing what all of the different tags do. The main difference from other types of objects in the game is that it uses "NextModule," not required module. This means that it is impossible to have branching asteroid base upgrade lines. It must be linear, with each module listing the next module in the line.

I don't know if the ai will build them, but I do know that when you put a space miner on auto, it will always go after unclaimed asteroids first. I have never seen it upgrade an existing asteroid, but that may be because I have never gotten that far in a game. If the AI uses the same code, then they will likely not upgrade their bases until late in the game, if at all.

I hope that was a little bit helpful.