It can be risky? I haven't messed with my ps3 in a long time and I never heard of that issue. Ive only backed up my data once and that was to move to a 1tb hdd from the 250 gb one that game with my slim. Maybe it would be a good idea for him to back up everything multiple times just to make sure?I don't think the PS3 can partially format/encrypt just the additional part of the HDD that was added in comparison to the old one.
But I don't have CFW (yet hopefully) so I don't know for sure, but also Wii U doesn't support this officially and there are also no hacks that could allow this.
The problem is that backing up the HDD via the official utility and then restoring it can be a bit risky, I lost my installed data because some part of the many 4GB files created by the backup tool were damaged, so maybe back your install data and saves up via FTP and then copy them over after formatting your new HDD?
The best way to upgrade us the method I mentioned above. Clean easy and simple. (With rebugs save data owner patch this backup method will also work to transfer from one PS3 to another)
BTW I use this method as I always tend to have trouble with the official backup methods (trouble that this easily gets around.) And like I said there are some benefits to this backup method. It can be restored even on a different PS3 and you won't loose any games or saves.