Hi, yep you can split them. If you want to retain the ball shape you'll either have to tie the two pieces into balls or keep rolling them until they make themselves into balls. you can also open them up, flatten them out and tie to logs, rocks etc for instant 'lawn'.
I have quite a few, none of the fish eat them but the shrimps and fry eat micro organisms that are in them. they are also great if you are cycling or cloning tanks - there's loads of friendly bacteria in them, i always chuck a few in when I start a new tank.