Hi,
The system did not allow you to change as it is a Header condition.Change the condition type ZRB6 to Item condition with the below changes.
In your DEV system in Configuration, tcode M/06 (Change view conditions- Condition types- 3rd screen shot attached by you) kindly check "Item condition" check box instead of the Header condition under "Changes which can be made".
Maintain the condition records accordingly and check.
Reg
Irfan