If you want to disable touch ID on the fly as is today (iOS 10), just use a finger that it doesn't recognize a couple of times in a row and then "Oops it wants my full passcode now"
I just tried this. On iOS 11 on my iPad, putting the wrong finger three times in a row prompts for a passcode, but, you can hit cancel and then use a correct finger and it will still unlock. So I don’t know if that helps you because it doesn’t require a password after three incorrect tries, just prompts you for one.
Five incorrect/bad fingerprint reads will require passcode.