Ok so now you're talking Actor Type instead of Actor Group? I may need a more detailed explanation of what you're trying to do.
My understanding is this -
1) You have the Health behavior attached to an asteroid
2) You also have the Inflict Damage behavior attached to the asteroids
3) You don't want collisions between asteroids to inflict damage on each other
To do this, you can create an Actor Group type attribute. In the "when collided" logic - check to see if the group of the last collided Actor (there's a block for that) matches the attribute that you created. If so quit out.
If you didn't want to limit yourself to one Actor group, you would create a List attribute and populate in the names of the Actor Groups that you didn't want to inflict damage. Then in the "when collided" logic, you'd loop through that list and check if the Actor Group of the last collision matches anything in your list.
If you wanted this to check Actor Types instead, it would be the same logic - just replace the group blocks with the type blocks.
It's possible that I'm completely misunderstanding what you're asking. If so, could you outline exactly what you want to do?