When you unload a loaded referenced object, it frees the memory but does not delete the reference.
Unload – If you have a reference object named NS, you can set its IsLoaded attribute to False to unload all the referenced items as follows:
lFileReference = FBFindObjectByFullName( "FileReference::NS" )
lFileReference.IsLoaded = False
Reload – You can reload the reference object by setting its IsLoaded attribute to True as follows:
lFileReference = FBFindObjectByFullName( "FileReference::NS" )
lFileReference.IsLoaded = True