It should be possible for a solicitor to draw up a definitive financial arrangement if both parties agree to the terms. However, if one party then does not abide by the terms the other one would probably have difficulty enforcing the agreement and would almost certainly need to start Court action to do so.
I don't know whether such an agreement would be regarded as binding by a Divorce Court judge if there was subsequently a divorce in which one of the parties wished to alter the terms. A solicitor could advise on this.