I'm afraid I don't think that scenario is possible or plausible.
Delaying or Suppressing the Louisiana Purchase would be possible if the French retain Saint Domingue (Haiti) as Napoleon could try to develop Louisiana as he had wished to. However, the US were eager to move westwards and Louisiana is in the way. That would be source of trouble for Napoleon later on. Not to mention Louisiana shares also a border with British Canada...
As for Mexico, there are little chances of Napoleon accepting the title of Emperor of Mexico or the Bourbons allowing it.
First, Napoleon was NOT the King of Spain after 1808 : he had given the title to his brother Joseph. This means Napoleon had no right on an hypothethical Mexican throne. It would be more logical if Joseph Bonaparte were to declare himself as Emperor of Mexico in hopes of gaining help from the Spanish colonies.
Second, Mexico supported the Spanish Bourbons against the French, depsite the fact they hated the way the Spanish (By this, I mean the people of Spain) were treating the Spaniards (the Spanish colonial people). Why? Because Napoleon and his brother Joseph were foreigners.
Lastly, Napoleon wouldn't be able to claim the title Emperor of Mexico after his defeat. One, he would have to get there, and the Royal Navy is in his way. Two, the Spanish Bourbons would want to keep their colony, no matter how ruinous it is to them. Three, there is the fact that he had no technical right to do so as he never ruled Spain or one of its colonies.