I agree with snowgirl's reflections on putting AD/HD on the Autism spectrum. I don't think it serves either population to do that because they require such different treatment.
Anyway, I don't think Asperger's is situational. I think it's a round the clock sort of thing. I also think that telling the principal that he'll act the same way the next day is an attempt to manipulate emotions. It certainly isn't nice, but it does reflect a certain amount of awareness of other's feelings. What would you do with an Asperger's diagnosis anyway? How would that help him? I can think of a lot of ways it could hurt him but right now, it sounds to me that you've got a lot to work with with the two existing diagnoses.
Has he seen a psychologist? Your doctor could help you find a psychologist that specializes in AD/HD and ODD. That would be my first move. I don't think AD/HD is the primary problem. I think you have to address the ODD. In other words, find out if he has an anger issue to address and if not, start a hard-core discipline program at home combined with a behavior mod program in the office. There's a book called 123 Magic that pertains to raising a kid who's been diagnosed with ODD.
