Two things
First use the File > Save As command. You will give the current project a new name. This will be a duplicate of the original. It will diverge from this point forward and not be connected to the original.
Second consider the File > Import > Research Files as shortcuts You import your pictures and can see them in the research section, but are actually using a shortcut and this does not massively increase your project size. However, if move the image on the computer you break the link. Organize your pictures on the computer before doing this.