Hello,
I'm sorry but i am not sure to understand your post.
Requirements can be lock
 

For instance if a major modification is done on a requirement, then we should have two versions of the same requirement.
If the change may impact the test execution result, then, the test case should also being modified leading in a second version of the same test case.
Therefore, one requirement version is always linked to - at least - on test case version. Sorry for not being clear enough. Best regards. #L.

Sorry we don't handle this case, you have to duplicate the requirement to do it