Don't shred the rockwool just drop the whole thing in a small container and loosley pack soil mix around it. I always start in cocoa plugs and transfer to the dirt same principle with 1" rockwool. Check my grow journal to see how I use a two cup method.
Your can use it to transplant into soil, no problem. Make sure you dont saturate the cube and you'll be alright..And know that most people use soil to germ seeds and rockwool for clones. Good Luck man!!