I like to change the VirtualMachine.Disk0.StorageReservationPolicy Property with a vRO Workflow based on CustomProperties. The Workflow was not a big deal but on which Lifecycle State must it run? I tried PRE VMPSMasterWorkflow32.Requested but this State is to late.
Storage reservation assignment happens during "Allocation" phase (IMHO). No way to make any changes in this phase, actually you can't even catch this even/phase.Requested-PRE is the very next step, when vRA already made all decisions about Reservation/Networking/etc. The only way to override this settings - to give end-user an option to select Reservation policy in request form.