Let's say a player casts a spell, completely allows it to resolve, and accepts its consequences - then realises that was a bad idea, or there was something better to do. That player realises there was a better card to play, or that the spell will do something they don't want to happen, such as deal enough damage to that player to kill them.
Does the caster have the opportunity to go back and fix that mistake (and to stay alive), even though they already accepted the consequences?
Depends on what you mean by "misused".
If the card was cast illegally, such as trying to Shock a creature with Hexproof, the game is rewound to the point immediately before the spell was cast. This does depend on how much time has passed- if so much time has passed that fixing it would be difficult, just correct anything currently illegal and continue the game.
If a player just did something silly, like trying to Shock a creature that actually had 3 toughness because of a Glorious Anthem, the answer is no in any tournament setting. Once you've taken an action, you can't suddenly change your mind. In casual play, it's up to the opponent. If the opponent decides it's sporting to allow take-backs, they can allow them.
It would entirely depend on the type of game you're playing.
If you're playing in any sort of tournament or other "serious" venue, you're SOL.
In a casual setting, it would depend on your opponent, I suppose. If they agree to rewind, then you're good.
But to put a proper answer in, strict RAW says that once you've done it, you've done it.
