Thanks for this. I don't see any mention of "If you change or alter the signature in any way, you will not be entitled to payment" in the original contract.

It is well accepted that contracts cannot be altered unilaterally without a suitable clause and consideration. If you would like me to cite case law from a variety of jurisdictions, let me know.

I believe DiceBitco.in's statement is invalid, as it is not part of the original contract.