Back it up using iTunes. That's one way to preserve it. Also depending on the iPad's age you might be able to rip them off without jailbreaking.
iTues will shut down this year so I'm not sure that's a viable solution.
Not sure about IOS, but on Android I bet you could get away with any (newer) OS version in 99% of cases. Increasing the "make sure we're running on ver.x" value in the app's metadata doesn't necessarily mean the code will also rely on new APIs. I bet the majority of apps on the store right now could run on much older phones if the SDK didn't force a somewhat recent version to check for as the minimum (beefy hardware requirements due to bloat and/or coder lazyness notwithstanding).but you would likely need the SAME OS version that those files match up to.