I did something similar once when I was freelancing. Knowing the company had some payment issues in the past, I modified the contract so that I could delay deli

I did something similar once when I was freelancing. Knowing the company had some payment issues in the past, I modified the contract so that I could delay delivery until I'd been paid in full (rather than invoicing upon delivery). When they inevitably didn't pay me on time the CEO called me up to ask why they hadn't received the finished product from me. When I pointed out I'd modified the contract - which he had returned, signed - he said in a rather hurt voice "...but I never read it - I just assumed it hadn't been changed!". There is a lesson there!