Yes, they're valid. What you are essentially doing is creating a counter-offer instead of accepting the contract as-is. The offering party is then supposed to

Yes, they're valid. What you are essentially doing is creating a counter-offer instead of accepting the contract as-is. The offering party is then supposed to review your modifications and accept (sign). If the employer simply doesn't do anything after the employee has made the modifications and returned the document, then they really don't have a leg to stand on.