If the design contains instances of any library or a particular cell, apart from the Liberty cell, it can be read-only, black box, or a reusable block. You can register those as reference libraries in the Reference Library Cells section on the Libraries tab of the Power Manager Setup form.
The cells in reference libraries are not edited during the 1801 import flow. If the input 1801 file has a connect supply net command for an instance inside the blackbox cell, the cell is not edited to create the netSet or any supply ports. During import, the hierarchy is traversed to map all the supply nets to the supply set at the instance boundary.