Hotels that don't let you pay more for a room than you actually agreed to when making the reservation are -pardon me- extremly stupid. If all conditions remain the same (non-refundable, non-changeble), why on earth should they refuse higher revenue; up to 50 % more than originally booked? The suite will most likely remain unsold anyway, and the actual minibar cost (except the few hotels that provide really expensive liquor) is minimal.

Two experiences: One hotel (IC Berchtesgaden) was happy to change my F&F reservation to another date and upsell me to a qualifying rate. Another (IC Cologne) refused to accept my additional money (called in advance) - bad luck for them, I kept my €€€.

I'd speak to the hotel and the revenue or sales manager as a last resort.