If you would like to make a copy of a fixture so you can make some changes to it without affecting other users it can be done from vrLibrary.
NB: If you make changes to an existing fixture they will be changed for every user who has used that fixture in their 3D Stores. When you duplicate a fixture the name will default to copy of fixture name and everything else will be the same apart from the internal unique ID of the fixture called a GUID.