Linden Lab Official:How do I get permissions back for something I gave to someone else?

Unfortunately, you cannot regain permissions for an object you have given to someone else. Linden Lab is unable to reset permissions on an object; the permissions you give the next owner are permanently marked as the most lenient permissions the object can ever have in the future.

If permissions allow, it is a good idea to create a backup copy of an object before you give it to someone else. This way, you always have a copy of the "most permissive" version of the object!

Important: Default permissions are no modify and no copy! Always check permissions before giving objects to others.