There are a list of operations that become not possible after you delegate a service plan to the reseller(s).
Impossible to delete the subscription period:
This Subscription Period is used in Delegated Plans.
Impossible to change the trial option:
You can't change period length or trial flag - this Subscription Period is used in Delegated Plans.
The same errors repeat even if this service plan is deleted from the list of delegated and the resellers get synchronized.
Impossible to change the billing period:
This Plan has been delegated to Resellers. You are not allowed to modify Billing Period Type.
1-2. There are related bugs - #PBA-34816 ("Subscription period cannot be removed from delegated plan.") and #PBA-34818 ("There is no way to delete subscription periods from delegated plans").
3.This is correct system behavior that billing period shall not be changed for the plans that are delegated to the reseller. The restriction is explained by the fact that the reseller is billed by the settings that are defined in the provider's service plan, which means the changes in billing for the reseller are made "on a fly" - as soon as the change on the providers plan is done (if it had been possible), so the reseller would be billed some price for 1 month, while all the resellers customer would be billed the same price for a year.
1-2. Set the subscription period as inactive
3.Clone the service plan and set the correct settings in the cloned plan. Move the subscriptions to the cloned plan if required.