These things are *always* negotiable. If someone really won't accept a booking unless the promoter heats the private dressing room to 72 degrees, then they probably don't need the gig.

During the short time I booked acts (mainly folk/ roots / world) for a venue, I occasionally saw some ridiculous rider demands, but only once had any issues over not being able to supply someone's exact catering requirements. More often than not, performers were perfectly happy to get a hot meal and a drink or two, and at least once the artists weren't even aware what their rider asked for.

Having worked on the other side, accommodation or catering is always worth asking for, simply because it cuts down on the cost of touring. If the response is a list of local hotels and a quote from a caterer, then it's Travelodge and Tescos...