When you use a lot of layers, you can accidentally be on the wrong layer and make a change and lose some data or make a change yo do not want.
I would make a folder for these, then make the changeable side, save it, change the file to read only in properties, make a shortcut to the desktop for
that file. When making the face side just open your desktop file for the face. When making the new face you cannot save the file, you have to "save as", then rename the file to reference the change.
This makes it easier for me when I have a lot of files with changes which are similar.