Off the top of my head, it would at best severely weaken the strength of the hash function. Instead of having to brute force to find an output that matches exac

Off the top of my head, it would at best severely weaken the strength of the hash function. Instead of having to brute force to find an output that matches exactly, you would only have to brute force for one that was sufficiently close, then use a greedy search to move from there to the actual key. The stronger you make the "closeness" guarantee, the weaker the function becomes to this kind of thing.