A developer is creating a Dataverse plug-in that must execute custom logic when an account's primary contact is changed. The logic requires access to both the previous primary contact's ID and the new primary contact's ID to perform a hand-off process in an external system. The plug-in is registered on the 'Update' message of the 'account' entity. Which is the most efficient method to access both the old and new primary contact GUIDs within the plug-in's execution context?