The only thing personally I would watch for if he does take it is just how large a lump it leaves if the girth of the rat is right he may have no issue with it even though the weight is bigger than recommended but as the others have stated he will either take it or refuse it but it is always best to offer and have it refused than not offer at all.
* Length does NOT include tails.
Rats: Age Weight Length* Equivalent Rat Pinkies 1-6 days 3-8 grams 1-2" Mouse Fuzzie Rat Fuzzies 7-13 days 9-20 grams 2-2.5" Hopper or Weaned Mice Rat Pups 2-3 weeks 21-30 grams 2.5-3.5" Large Mouse Weaned Rats 3-4 weeks 31-45 grams 3.5-4.5" X-Large Mouse Small Rats 4-6 weeks 46-79 grams 4.5-6" Medium Rats 6-8 weeks 80-149 grams 6-8" Large Rats 8-10 weeks 150-265 grams 8-9" 1/2 lb Rabbit X-Large Rats Adult Rat 266-360 grams 9-11" 1 lb Rabbit XX-Large Rats Adult Rat Over 361 grams 11" + 1.5 lb Rabbit
Here is a chart that may help next time they offer you a different size than you asked for. Let us know how he does.