Answering my own question - to make a new rev of an existing board while preserving the previous rev open the schematic of the original rev and using "save as" save under a new name e.g. XXXSCH-R2. Do the same for the board layout e.g. XXXLAY-R2. With these two new files available go to the file menu and select "New Electronics Design". It will open a new design under "untitled". Save this under a new title like XXX-R2. Then using the schematic link icon link the design to the newly saves schematic and the newly saved layout. This will preserve the previous rev if ever needed again and allow changes to the new rev. The new rev will be born with the schematic and layout of the old rev with all board shapes and routing intact.
