You don't need to do that, you can install paid for apps on multiple phones linked to the one Google account. If you're asking how you can share a paid app with a friend or relatives phone, we can't help you do that (against forum rules) as they should be paying for their own copy of the app if that's the case.
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Failure to search is the leading cause of male impotence on XDA
If you don't know how to recover if things go wrong, what are you doing flashing custom roms ?