I believe you can change some per-unit parameters like collision box size, but mostly it's up the engine.
That's... not what I mean. Planetary bodies used to take chunks out of eachother and deform terrain/create craters/etc. I haven't seen terrain deformation like that since Tiberium Sun, and want it back as it was a severe game changer and modified the playing field.
I'd say what's even more broken is infinitely respawning one hit planetkillers. To my mind, either you have asteroids and craters, or no asteroids and no craters. It would be nice to have both, despite whatever issues craters have.
Craters never worked well and caused a big performance hit on the sim so they were removed. I have an alternative that I hope to one day implement that avoids the performance hit with craters and large scale dynamic terrain deformation. Like my original post without the actual craters: https://forums.uberent.com/threads/my-wish-list-for-asteroids-and-planet-smashes.69148/