So let me get this straight - you requested a stay, he didn’t want to accept it at the posted price, then you and he settled on a higher price than posted. You ignored the “red flags” of him asking for a higher price and decided to go with him anyway. Now you are cutting a week off your stay, and you are upset because he won’t accept your change request and tells you to cancel and rebook instead. You don’t want to do that because he might raise the price on you before you rebook your shorter stay.
I would not be surprised if he raises his price when you cut your stay short. He negotiated a price with you for a particular set of dates and may have given you a discount for a longer stay that he won’t give for your new, shorter stay.