As we reported just earlier this week, MuscleNerd was working on an update for redsn0w that would allow iPhone 4S, iPad 2, and The new iPad (A5/A5X) users to downgrade their firmware if they had their SHSH blobs saved. iPhone 4S and iPad 2 users have the ability to downgrade as low as iOS 5.0.1 and The new iPad users have the ability to downgrade as low as iOS 5.1. A4 users have been able to downgrade since the dawn of time due to a shiny bootrom exploit.
Originally Posted by Dev-Team
The new feature allowing A5 iOS device users to downgrade their firmware can be found under Extras>Even More>Restore from the redsn0w navigation menu. To use this new feature to downgrade your A5 device, you must have your SHSH blobs saved. For example, if you want to downgrade your iPhone 4S to iOS 5.0.1, you must have your iOS 5.0.1 SHSH blobs saved. Apple is no longer signing iOS 5.0.1, so if you haven't saved them already then you won't be able to save them now. Apple also has the ability to patch this downgrading method in a future firmware update, so take advantage of it while you can.
Another warning that the iPhone Dev-Team makes us aware of is since the new downgrade measure updates the iOS firmware before downgrading, it will update your baseband. For this reason, if you are relying on an unofficial iPhone unlock, do not use this new downgrade method until a workaround can be found. If you used the SAM technique (now patched by Apple) to unlock your iPhone, then you can use this new downgrading method without losing your unlock.
One last warning from the iPhone Dev-Team is since the new version of redsn0w is built with a ton of new code, they recommend using the more stable redsn0w 0.9.10b8b unless you plan to be taking advantage of the new downgrading feature. This will give them some time to work out the bugs. There is no reason to run this new version of redsn0w over your existing jailbreak because there are no improvements to the jailbreak in the latest version of redsn0w.
If you are ready to finally have the freedom to downgrade your iPhone 4S, iPad 2, or The new iPad, then you’ll definitely want to download this new redsn0w release. Be sure to thank the iPhone Dev-Team for this amazing news!
Sources: Dev-Team Blog