Sorry for being long-winded here, but I'm writing off the top of my head.
Seriously, the behavior you're describing sounds like something straight from a Mrs. Piggle-Wiggle book. Have you read those? You should! There are four of them. You'll laugh, and then you'll think. Your son is seven years old and he's doing what you'd expect of a three-year-old. The reason he's succeeding is simply because you're letting him win the game. Perhaps the thing every child does BEST is testing his/her parents!
In order to end his game, you have to have a game of your own. Quit worrying and start to be in charge. I'm NOT saying to be mean - I'm saying to go back to being Mama! And, for a while, Mama will have to be impressive.
If he were my son, I'd talk to his teacher first, and see how he behaves at school. If he doesn't behave that way, then you've just learned something important. Let the teacher know what is going on at home and get her on your side, because one day when your boy can't get his act together in the morning, he may just have to stay home!
Then I would make an doctor's appointment for my son and take him to it. (I'd let the doctor and the office know what's going on when I call. This won't be a first for them.) I wouldn't discuss it with my boy first; I'd just do it. You want to sound friendly and firm - just like a mama in charge. "Yes, you need this. You aren't able to listen, you aren't able to obey, you aren't able to talk like a seven-year-old, and you aren't able to get your act together in the mornings, so I guess you must be sick!" If he changes his act abruptly, don't be surprised, but stick to your guns. Don't let him argue or fuss with you. You're not being mean, but it's your job to take care of him. If the doctor says he's physically healthy, you can cross that off your worry list, and the cost of the office visit can be worth it.
When your ask your boy to do something and he says, "Kidzy is too tired," you can say, "Oh, poor Kidzy. Kidzy must need a nap. Into bed with you." Turn off the TV or stop whatever else he's doing, take him to his room, pull up the covers, turn out the light, and tell him he must stay there until you get him up, because that's what mamas have to do with toddlers. No books, no toys. It needs to be B-O-R-I-N-G. Give him five minutes or so, and then go in and ask, "Is (your son's name) able to be himself now?"
Tomorrow for breakfast, serve him the proverbial two choices: take it or leave it. Don't ask him what he wants. You are not his waitress. If he won't eat or come to the table, take the food away. Breakfast is over. (Snack time is for kids who miss their breakfasts. He won't starve. And you're not being a tyrant. You're getting him out of his game-playing, don't forget.)
You could try sending him to bed fifteen minutes earlier tonight, because toddlers have earlier bedtimes. After all, if he can't get up on time, he won't be dressed on time. If he doesn't dress and clean himself up, he won't be on time for breakfast. If he misses the bus, it must be that he's... sick. Back to bed, son!
What if he acts up like this when you all are out and about? "Oh, poor boy! I guess we'll head home right away so I can put you in bed until you feel better. No treat today!" Then do it right away. Make it an action, not a threat. (You can actually say something better than this. Just make it short and sweet.) Let him realize you're not playing his game any more.
The idea is that YOUR game has to be a little more impressive than his. (Once you stop worrying and start taking charge, you're going to find some of this very funny. But don't let him know that yet.)
A major problem with this kind of childish misbehavior is that it disrupts other lives. You don't say whether you have other children or whether you have other time-sensitive commitments. So I hope you'll be able to end his game really soon, because dealing with it can be quite an inconvenience. If all goes well, it could be just a day or two before he concedes. That doesn't mean he won't try it again at a future date!
When he starts being back on a seven-year-old track, stay in charge by laying out a plan with him. You could make a chart for him if he likes putting stickers on charts. He will see everything he has to do, in the order of doing it. He can make things easier for himself by laying out his clothes and his school things the night before.
Once HE starts playing YOUR game, you can go back to choices-for-breakfast if you want. But let him have the security of knowing that Mama, who loves him, will do what's best for him no matter what. Be very sure to tell him how absolutely DELIGHTED your are to see your real son again, and how you hope that awful, whiny Kidzy person never comes back.