Group commands are a type of command that can be executed multiple times at once. Group commands can be used for things like copying and pasting, rotating objects, or scaling objects.
SHIFT + G = Create a group from the items you've chosen.
Choose two groups. [Note that if they are difficult to pick together, you can use Select+Ctrl to add to a Selection.] Then right-click 'Group' in the context menu.
If the two groups don't collide with other geometry before pre-exploding, Explode the two groups you've chosen.
Edit one group at a time.
It's best to form groups as you go. Using a shortcut makes it a breeze. Remember that anything that is repeated (even mirror images) should be built as a component, so that if you alter one, the other changes as well, saving you time and effort.
You can do this with the Move tool if you try to push/pull all of your surfaces along the same axis. Double-click each of the faces (selecting both the face and the edges) while holding down the Shift Key to add the other objects to your active selection group.