The original officer rank and above has built in officer chat permissions. By copying rights from this rank while making an rank, they will automatically gain access to the officer chat.
So when you create a rank, if you want it to have officer permissions, base it of a rank that has officer permissions. If not, base it from a rank that doesn't have.
(Yes you might have 3d highest rank without permissions and you want to make that your 4th rank and create a new 3d rank. My suggestion is that you copy the rights from the 3d rank which will put this new created rank as 4th. Rename both of those rank and all people that were rank 3 and you wanted as rank 4, demote them.) That is the easiest way I've dealt with it so far but then again, my guild doesn't have over 50 memebers so it was an easy yet stupid task.