IOS – Share IOS app twice between Apple ID’s

I believe this depends on they way the App is set up. If an app backs up its data on iCloud then it will not be able to retrieve it as each Apple ID has separate iCloud storage space. On the other hand if the app uses its own server for syncing (and you use the same login details) I would imagine it will restore data appropriately. However purchases made with one Apple ID are not available to another Apple ID. I am not sure if Apple offer transferring purchases but I guess you could contact them to see it they could do so for you.

1) I don't think changing Apple ID will cause any data loss. I switch between two and never had any issues (I would however check with Apple) 2) Yes, but you might have to download them first if not already on the iPad. 3) This could happen as the apps will have to be updated and since iOS5 most apps have heavily changed both visually and the way they work with say iCloud. 4) As stated in (1) I don't believe you should loose any data but you can only have one Apple ID active at a time.

Make sure you take a full backup on your computer before making any big updates like moving to iOS7 from iOS5.

The answer is mixed. While the iTunes app store can be signed into with a separate Apple ID, there will be some data (naturally) stored on the second account you use. The device will not be added to their My Apple Devices, though it will become an Authorized Device in iTunes Store. As such, some level of data will be held in the Apple Servers to facilitate this transaction. AFAIK this data is not user-accessible.

However, for data backups, Photos, Find my iPhone, My Apple Devices, etc. that would require the user to login via iCloud on the phone and not just the Apple Store. From there, whatever level of data you set to sync would be replicated up. Please note, you CAN be signed into a separate iCloud and iTunes account, as well as various other services (such as separate iCloud and Messages accounts).