With the recent coming to light of the glitch on WH 1-23 in Angry Birds Seasons (Special Thanks to @donnmega for the detailed writeup on that!), and the fact that most members here have already updated their devices to versions of the game that apparently no longer feature this glitch, we have been faced with a unique situation that has been debated long and hard by many prominent members of our community. No need to rehash all of that here, there were many valid points brought up on both sides of the issue. I believe I may have found a solution that will make most everyone happy. It is possible to reload a prior version of the game and play the glitch level without losing existing progress, or even having to Jailbreak the device. Below I will go through the steps I followed to accomplish this.

First requirement - your iTunes account must have been used to purchase the app, prior to the release of the updated (non-glitch) version of the game.

Second requirement - you will have had to have synched your device, or otherwise downloaded the apps to a computer back when the older version of the app was the current one.

Third requirement - you must have actively saved your old .ipa files, or not emptied your recycle bin for quite some time.

Steps to follow -
- Backup current progress on your device using the instructions found in the ultimate backup tutorial
- Open recycle bin on computer, and choose to restore all angry birds files to their original locations
- verify that the app version you want is now located in the /iTunes/iTunes Media/mobile applications folder on the local harddrive
- In iTunes app library, click on the app you want to revert to older version of, and press the delete key, when prompted, choose to save the files in current location.
- In iTunes, choose add file to library, and browse to find the older version of the app, in this case I wanted seasons version 2.4.1
- On device, delete current version of the app
- Connect device to computer and allow to fully synch
- If older version of app does not load to device during synch process, click on device, then pull up apps, and browse list of available apps and choose to install to device and click on the apply button

At this point the older version of the game should be installed on your device, to restore previous progress follow remaining steps:

- Open app, and play one level through to the level complete screen, does not matter how many stars are earned, just that level is completed and a score is recorded.
- hard close app
- copy .lua files for the app from the backup created at the beginning back to the appropriate folder on your device
- reopen app and verify that progress indeed transferred
- Play glitched level until desired score is obtained
- update app back to current version using update feature in iTunes

I used this process on an iPhone 4, and an iPad2, both with the most current iOS installed, and it worked perfectly, without having to jailbreak the device. I believe the key to the process was that I was reloading my own app files, which had already been attached to my unique iTunes user ID. Special thanks to @estar for suggesting that I look in my recycle bin for the old app files! You are a lifesaver!