I came across this post in the Apple developer forums, and thought other CoronaSDK developers might be interested.
https://devforums.apple.com/thread/144061
see post #19 in this thread for details on how to update your environment so that you can still use Xcode 4.2 to load your apps on a iOS 5.1 device.
I would suggest you have an up to date backup if you plan to try this, just in case something goes wrong.
I have followed these steps and the only problem that I ran into was the xcode_4.3.1_for_lion.dmg would not pass VERIFY on my 10.6.8 machine. I had to mount it without verifying it.
So far I have not encountered any other problems and I can load my developer builds of CoronaSDK apps on an iPhone running iOS 5.1.
[import]uid: 67839 topic_id: 23264 reply_id: 323264[/import]