@tbraxton has the right answer here but to expand on the answer:
1. If you don't have access to skeleton models you can use just an empty part model that holds your CSYSs or just place a bunch of CSYSs at the new assemble level.
2. Once you make your new assembly and skeleton, assemble it into your existing assembly. Then activate the skeleton in your new assembly. Then create a new CSYS feature and place it on top of the electrical box default CSYSs. Before closing the dialog box click the skeleton CSYS. This will then cause Creo to copy all of the CSYS transformations into the new default CSYS without the need to make a transformation matrix measurement. After you have closed the new CSYS dialog box you can now go back into your new assembly and assemble the electrical box on the new CSYS that you made in the skeleton model.
