So I put two planets on a collision course just so they basically cut each other half at the very beginning of a match. You then are playing on half a planet! Only issue is that units can still go to the spot that is gone and the surface is invisible.
hmm when I tried to do similar stuff by applying a big subtractive csg brush it horribly failed with endless planet building and extreme memory usage. Guess I maybe used a too complex brush or something. Nice!