If you are already on CFW then all you gonna need is just insert the new hard disc which you bought and install the same version CFW firmware of your choice before you had it (i prefer Evilnat cfw).
Also check QA flash is enabled before switching firmwares if you are going to a lower CFW firmware or else this is not needed to check if you want to be in the same CFW firmware (minverchk 3.55 or below consoles only).
yes after inserting new hard drive into PS3 , just do the steps as normal as we do install update file (Evil nat 4.89 cfw cex firmware) from recovery mode.