Not sure I understand what you mean, can you confirm it this is what you are trying to achieve: disable the ability for end users to create or delete DGs, but allow them to manage the ownership of exiting groups? In this case, toggling off the MyDistributionGroups role, but keeping MyDistributionGroupMembership is the solution. Give it an hour to replicate and test, but make sure to log the user off and back on first in order for the updated role to be reflected.
As you can see from the MyDistributionGroupMembership role definition, it includes the required cmdlets to manage membership:
If you need more granular control, you will have to create new roles based on the MyDistributionGroups/MyDistributionGroupMembership ones and edit the set of included cmdlets as necessary.