On the topic of Fire Emblem: Heroes, it looks like Nintendo's got no tolerance for those who think they can get a leg-up in the game by cheating. No, sir.
In a recent update, Nintendo slipped a message in for all to see. While they didn't call out anyone in particular they certainly addressed it to the guilty party.
"Thank you for playing Fire Emblem Heroes. Since the release of the game, we've detected improper use from some players. Countermeasures are being employed to address this, including temporarily limiting access to certain features.
Players who are subject to these countermeasures will receive a notification in the 'To you' section of the game's notifications. We ask all our players to abide by the User Agreement, including the Code of Conduct, as they continue to enjoy Fire Emblem Heroes."
Whilst that isn't exactly threatening a permanent ban, it's probably best not to cheat and annoy Nintendo. You'll just have to slog through the game like the rest of us.