If you use the codes you have to pay for them.
Easy as that.
No.
If you use your CE codes, you're not still obliged to pay for the CE itself. I have my CE codes from Play, and I will use them for the Headstart, but I can still go ahead and cancel my order from Play if I want. Or I can just cancel my order from Play, and still go ahead and use my Headstart codes without shelling out any money.