No. I belive you are refuring to Target Prioraty fromt eh old edition.Do units still require a leadership check to shoot past an enemy unit?
Can models with sniper rifles pick out a unit in an enemy squad to shoot?
Can a Lord Commissar join a unit that is not the CCS?
No. You may only allowcate your oppoents wounds if you have a special rule allowing it such as Telion.
Don't play Imperial guard so i can't help too much here. Also don't know what CCS is? there is not abriviatoon box to explain.