new document splitting characteristic for general ledger

Hi

We using the ECC 6.0 version and we have activated the Segment as document splitting characteristic for general ledger but now my client is asking to activate the new splitting characterstic as Profit center.

How system will consider the this requirement since we already posted the transactions and we have a old splitting characteristic ( Segment )

Please suggest me to complete the above requirement and what are steps require to active the new splitting characteristic.

Thanks

Risha