if you have a slim or a later version of the phat that has 16MB of flash it depends on how you format your drive it you format it via the ps3 then no you wont have to but if you format if via pc or some other way then yes you will have to reinstall your current firmware or later.
I'm still slightly confused.. I intend to format via ps3 xmb. It's early phat model.If I do not have to reinstall CFW how do I go about reinstalling packages ie multiman? thanks
backup your HDD first by internal $ony backupTool... format your Disk and restore the backup... I did it that way a few weeks ago because HDD replacement...
after restoring my backup... all "selfcreated" folders where available after that ^^ even MM and GT5 were available after that