Sure, it's supposed to be difficult. It's already difficult!
The problem with an accidental hammer-grab ending, or worse, nullifying, your whole game is that there's no logical justification for it, other than strictness for strictness's sake. You can make the argument that a hammer-grab invalidates continuing, but you can't argue that it somehow invalidates the score you accumulated thus far. There's no precedent for that in any other DK track that we play. Tougher doesn't automatically mean better, and in this case, I think it hurts the track.
My interpretation of this challenge is that you're supposed to get as far as you can without using the hammer in the process of clearing any boards. If you accidentally grab a hammer, okay, kill your guy and redo the board. You're still holding to the underlying "no hammers allowed" principle, and you still have to complete 116 boards the same as the guy who never grabs one. And it's semi-rare anyway. You're not gonna do it every game, or even every 20 games.
I'm just thinking about this relative to protocols in other games and sports. Grabbing a hammer in a no-hammer run is akin to a foul. In most games, fouling just gets you a penalty. To be DQ'ed, you actually have to show ill intent, like intentionally cheating, or something happens to render the game unplayable or to have been compromised from the outset.
Soccer, for example, is a "no hands allowed" game, but if somebody DOES use their hands, you don't declare the entire game null and void, or end it then and there. You give the offending team a penalty (the other team gets a direct free kick) and you keep going!
It's definitely too late to set it up so that the penalty for a hammer grab is a lost life and a forced "do over' of the board, as opposed to an instant game over, but I don't think it's too late to at least make the score acceptable up to the point of the grab.