I regret choosing to play Mount & Blade in hardcore mode. Is there a way to turn it off?
There isn't a way to do this, unfortunately, unless someone goes and deciphers the savegame format and figures out where the hardcore mode flag is.
What you can do though, is export the character, then import them into a savegame that is not on hardcore mode.
If you do this, you keep your skills, attributes, money, and experience, but you lose your reputation, honour, army, and items. Its not really a great method, but if you're attached to your character, its a better alternative than starting over.
Here are the steps to take to export your character and import them into a non-hardcore save:
I know this isn't exactly what you want, but its about as close as you can get.