Neri was appointed "head of security" in the novel. But, in GFII, it's Rocco who seems to be "head of security"--and that wasn't, to my mind, a good place for him relative to Neri. You see Rocco constantly scanning the crowd at Anthony's party while Neri is nowhere to be found. But then Neri turns up in the meeting with Johnny Ola. He introduces himself as if he's a full partner in the ensuing discussion (which Tom is not invited to attend because "Tom won't be sitting in with us today--he handles only specific matters..."). Meanwhile Michael dispatches Rocco: "Johnny's men look hungry--why don't you take care of them"--as if Rocco's a caterer in addition to being head of security.
As I've posted a hundred times: a subplot of GFII is how Neri tries to push past Rocco and Tom to become Michael's number-two guy. These and other examples show that he pretty largely succeeded (although "number-two" is meaningless in Michael's domain--there's Michael and no one else).