Gan fod y CPTPP yn gytundeb masnach sy'n bodoli eisoes, ni fyddai'r trafodaethau'n dechrau gyda dalen lân: byddai gofyn i'r DU, i bob pwrpas, ymuno ar y telerau presennol. O’r herwydd, er bod modd ceisio cael esemptiadau ar gyfer meysydd sensitif drwy lythyrau ochr a throednodiadau, mae'n debyg y byddai'r cytundeb, i raddau helaeth, yn aros fel y mae.
As CPTPP is a pre-existing trade agreement, negotiations would not begin with a clean sheet of paper:  the UK would be required to join broadly on the existing terms. For this reason, whilst it is possible to seek exemptions for sensitive areas through side letters and footnotes, the agreement would probably largely remain as it is.