It is possible to install 2 versions of the same app on your device. However, you're the one who gotta edit the .ipa, and it will lose its on-line features, like syncing with Facebook or something else.
Matthew Frederick said on his answer to your post:
"but it's the bundle identifier inside the app that identifies it and allows the OS to know it's supposed to perform an upgrade. The developer has to keep the bundle identifier the same in order to actually provide an upgrade and not a new app"
You can edit the bundle identifier, and here's a guide on how to do it:
Let's suppose you have the version 2.0 of the app installed on your device, and you want the version 1.0 also.
- You'll need those following programs on your computer: "WinRAR", "plist Editor Pro" and "iFunbox" (the last one is to install the older version of the app on your device)
- Download the version 1.0 of the app (.ipa file) from the internet.
- Search for an app that you would NEVER want to download, it doesn't matter what it is, and download its .ipa .
- Open this last .ipa with WinRAR.
- There will be a folder called "Playload", open it.
- There will be a folder with the name of the app, open it.
- Double click (to open) the file "Info.plist".
- Search for "< key>CFBundleIdentifier< /key>", without spaces.
- Under it, there will be the identifier, for example: "< string>com.company.appname< /string>", without spaces.
- Copy this "com.company.appname".
- Close the file.
- Now open your app's older version's .ipa with WinRAR.
- There will be a folder called "Playload", open it.
- There will be a folder with the name of the app, open it.
- Double click (to open) the file "Info.plist".
- Search for "< key>CFBundleIdentifier< /key>", without spaces.
- Under it, there will be the identifier, for example: "< string>com.2company2.2appname2< /string>", without spaces.
- Replace this "com.2company2.2appname2" with the one you've copied earlier.
- That will make your device think it's another app, and not simply replace the one you had with the one you'll install.
- Save and close the file.
- If WinRAR asks if you want to make the modifications, press YES.
- Now open iFunbox, and plug your device into the computer (close iTunes if it pops up).
- On the top left hand corner, press "iFunbox Classic".
- On the left, open "Connected Devices", then open your device's name (for example, "Johnny | New iPad on USB"), then open "User Applications".
- On the top, click "Install App", and select the .ipa you've just modified.
- Wait for it to install. Make sure the device has its lights off (locked).
- Enjoy the 2 versions of the app on your device :)
But again, don't forget this disables the on-line features of the app, because of the bundle identifier change. Also be careful not to install the app from Step 3 as this will cause an upgrade.
That's the only way I could figure out to do this. There may be other ways.