Module ChangePlan Validation
With regard to Product Configuration Options, there does not seem to be any way to validate that a change may be performed prior to actually performing the change.
I propose adding either a hook point for like BeforeConfigOptionsUpgrade which would be run before modifying a products configuration options or adding a functional call in the module cycle for ChangePlanValidation or something similar.
Expected results from the former would be a true or false, from the latter would be 'success' or an error message to maintain consistency. Failure / error would result in returning to originating page with error message.
Real life example: Customer has a product for cloud storage, with product configuration options used to add additional space. End client wants to downgrade their space, but is already using more than what they are requesting the change to. This would result in a failure on the server provisioning, but should be caught prior to failing.