i'm not entirely sure this is hardcoded. I know that the reference entity files for the crystal and metal asteroids is in the gameInfo folder. And i am guessing at this point that like strikecraft it may be possible to change the internal parameters fo the entity to reflect something else... like giving bombers missiles as weapons, perhaps a crystal/metal hybrid resource asteroid, or something new you create and list in the string folder, such as say black ore. But would have to experiment with this to actually see what happens in game when we make such changes and if they are recognized or not.
On another sidenote, with the devs changing some of the abilities using anti-matter, crystal, metal, credits (resources), they may be considering adding "new" elements or variables with the expansions. A craftwork system, where differrent elements might be combined might be interesting. Or a conversion of one to another at a percentage basis might be interesting as well, currently they only convert to credits, or from credits of course to metal or crystal.
Something to give a try with though, and something hopefully to look forward too, if the devs are really considering adding some new things. 
I will look into it and let you know what happens,
Take care,
-Teal
