yep, but you dont need it the tiny amount of pressure you put in them for the priming part of the cycle is only to prevent the bladders from being damaged and to give the oil some guidance. If you have to you can do the rest of the work with a hydraulic press and a set of known lengths for things to be. doing it on the vehicle just has it all mated up and lets you set the overall pressure to suit the way you want the boge to handle.
you dont need to completely purge and bleed the pumping section ,just get enough oil in it to make it start pumping and provide a good consistant seal around the piston without aerated oil while its trying to get itself sorted out.

