While the Driver Control flag for an equipment type is theoretically eligible to be updated, changes will not be allowed in the following cases:
Change will not be allowed if it would create a conflict situation between Team Driver flag for a Tariff Service and any of the Equipment Types enabled for that Tariff Service (if Team Driver for the Tariff Service is True, none of the equipment types enabled for that Tariff Service can be "Single Driver Only").
Change will not be allowed if the equipment type is defined as the Default Equipment Type for the system (in Global Settings).