In a previous job, providing banking services to soldiers in places where there's no banks, I always ended up with a bunch of badly written cheques from semi-illiterate squaddies.
So, being lazy, instead of chasing each soldier up and trying to find where he was, I'd just make the changes myself - using a similar pen to the one that the soldier used - and scribble what I thought looked like the initials of the soldier by the amendment.
Never had a problem and I must've done this with hundreds of cheques.Obviously adding zeros and increasing the amount wouldn't be very clever.