(adsbygoogle = window.adsbygoogle || []).push({}); If I buy a new hard drive I can dO jailbreak??

No, firmware is stored on the nor or nand chip(whichever your console has. the only way to downgrade to install jailbreak is to get something like a e3 flasher or progskeet which requires you to take you console apart

if all your looking for is modded games on 4.00 just send your hard drive to someone that has a 3.55 and a 4.00 that will data transfer mod re transfer and send back to you. they just put your hard drive in there 4.00 so that way you keep all your info and game saves and data transfer to 3.55 so it wont make you format. Now all your stuff is on a 3.55 and ready for mods then transfer back to 4.00 on your hard drive and sent back to you

Since all is basically explained above, the simple answer is no. The Hard drive only stores memory.

No it is not possible