It is keeping in memory but what about making it blank string and checking it in code to ignore if it is zero length string?
I think since it is capable to register new keys should be able to unregister them. At least the those that are inside of the <attribute name="Properties"> tag. And I did not mention the loaded files by the <attribute name="URLList"> tag. You can modify the, you can stay in head but still nothing. But anyway, good workaround.
Thank you for your reply.