You have to upload files in the Mods/Scenarios section of Shrapnel, then post the link to them in your post here. You don't have to make a post in Mods/Scenarios, just hit "Add New Topic" or "Add New Reply," then hit Upload File Form. Upload the file, copy the URL, then paste it in your post in here.
The Dark Matter asteroids are not actually used anywhere.
Altering them has no effect.
I am not going to remove the damaging asteroids from FQM. You could always mod the AIs to not build Storm Destroying devices, which they don't really need to make in the first place.