The process of change can be controlled and managed in a predictable way - this will cost less and be quicker than 'being organic'.
As well as contractual changes, other streams of work will include financial impact analysis, modelling, business change and systems change. The level of change required will depend on the contracts you have in place, their values, the change caused in switching to RFRs and the capability of systems/business teams to support such changes.
Not all contracts will have to change. Some contracts will not have any material impact, either because of timing or value. However, most will have amendment clauses that will have an impact on both parties to the contract. Contracts should be delivered on a prioritisation basis.