The way I understand it, the 10% rule is for hatchlings and growing snakes. When they're young they need more food to grow, but once they get close to their adult size they don't need as much, so you want to slow down on increasing the size of their prey. Your snake isn't at adult size yet, but he's getting there. A 50 gram small rat is all an adult male ball python will ever need, no matter how big he gets. So while 50 grams is an ok size for your snake, you don't want to go above that. He's getting to the point where 10% is too much.
It sounds like you have weaned rats, which are just a size under small. So just feed him the rest and get small rats next time. While I don't think it would hurt him to feed him two rats at once, it might cause him to stop eating for awhile. Ball pythons are notorious for skipping meals for a lot of reasons, including being overfed. Smaller meals now will make him less likely to refuse food in the future.