In the same way, and to be aligned with the next version of reviews (Feature - review process of risks, policies and assets), after the creation of a New Audit, the “Planned Start” date should be disabled, the user can no longer modify this date. You can still show this field to the user (read-only).
I struggle with this - on one hand, yes, a planned date shouldn’t be changeable, but then again, it should. Prioritizies and resource allocations shift all the time and the user should have the flexibility (or perhaps, option via customization or a permission) to make modifications.