The K balls come in the original packaging from the mfgr and are opened by and in the custody of the officials. They aren’t massaged by the teams like the playing balls.
I've also read they are in custody until shortly before the game starts, then given to an attendant.
League confirms ball-deflation investigation
..........."Several years ago, in an effort to prevent any doctoring of balls used in the kicking game, the NFL adopted a rule that six new, specially-marked kicking balls would be used for each game, with the boxes opened by the officials two hours and 15 minutes before kickoff.
All balls remain under the supervision of the referee until they are delivered to the ball attendant shortly before kickoiff."....................