<--- PE
The owner doesn't have to change the design, he just needs a PE to review and stamp it. Or if it's the type of design that was done IAW codes with no particular engineering required and didn't really need a PE in the first place (which sounds like the case), then the new EC should have just as much authority to approve the design as the one who originally drafted it- the new EC would have to check everything, and would be assuming the liability for the design. Or at least that's how I'd see it logically. Now, legally? ...who the hell knows, everyone's probably liable to get sued if something goes wrong.
...and before you ask, my license is in VA, not CA, so I can't help you, sorry!
