Can you enable a intercompany segment if you have not yet established one on an existing accounting

We need a way to account for additional internal business units in our general ledger.  We have used all 9 segments of the balancing segments, and only set it up to have a length of 1.  We have never identified an intercompany segment flexfield qualifier and are hoping we can use this feature.  The current accounting flexfield is frozen and active.  We want to use an old segment that is no longer used as the intercompany segment but we have to unfreeze the flexfield to do this.  Looking for risk, advice, guidance.

Thanks,

Tracy