Renovation - clarify contract point of dispute

[Vlad Selsky]

My general contractor and I signed a contract to gut and renovate two rental properties for a fixed amount of $170K. When it came time to buy the kitchen cabinets, he budgeted $2000 per unit. After I spoke with him, he gave me the go ahead to buy cabinets of my own choice. I paid out of pocket well over double for much better quality. Of course he still received his labor fees for the cabinet install.

All of the contractor's items have an 18% markup for profit, contingency, etc. I'd like to understand if there is a business best practice for this question -- should the $17)K contractual amount be reduced by $2000? Or do I still owe the contractor the 18% on $2000 that he was anticipating pocketing? In short, in case the amount matters, it's only $720 (.18 * 4000).

Thanks, Vlad