A backup of a game would be a save file. Are you talking about a .cia/.3ds, that is a game that was dumped in a format that allows playing on the 3ds? Sorry if the jargon's confusing, but you're a little confused on some terminology, but that's fine
You can install and play .cia files when you downgrade to 9.2 other than that you can't get into cfw (Rx"tools").
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Bro. No one "plays" backups. He was using it in the wrong context. If a backup=dump of a game in his sentence, then I guess he'd be right, but no one says that.