If there's LUA code to move asteroids, I haven't found it - and believe me I've been looking !
It does seem to be possible to change an asteroid's radius and send distance in Function Level Logic, though. Send distance works for sure as I have this working in the level I'm working on. Haven't tried asteroid radius yet, but with the mathematical functions included in the LUA language it should mean it's possible to create asteroids that grow and shrink over time, or depending on how many seeds or trees are on them. The idea of having "pulsating" asteroids seems pretty cool, and not something I've seen in any levels so far.. :>