I would fear that loading in two lighting bricks causes issues, so you would need a base scene without lights as well to use them from a contract.
Did somebody test using these scenes from a contract and verified that does not cause problems? Or do you need the registration for something else?
From looking at the Sapienza ones, it seems that the intended way to use these bricks is to use them from scenes, not from a contract. That does not require a registration in packagedefinition.txt and is already supported by the current version of the framework.