I would document the business reasons for a change in terms of functions, assets and risks and why the new system reflects the most relevant transfer pricing methodology. There should also be documentation to evidence that the prior system/method was the most correct method, any change in facts/circumstances that prompts such a change and how the new method accurately reflects the revised relevant business purposes for your transfer pricing. Transfer pricing documentation should be prepared in the relevant jurisdicitons, under the old and new systems/methods, to provide the required evidence re: functional analyses, economic comparables, description of the business, etc. that mitigates related tax risks/penalties.