I'm going to leave aside the several aspects of this which makes it highly unlikely to happen (the British government would want a man who embodied the destruction of their political system, and who was popular with the British public nowhere near London / Napoleon would not opt for a menial military advisor role over even the negligible power of being Emperor of Elba [his actual title] / Wellington and most of the senior officer corps would resign en masse in protest / he had no need for extra medical aid as the British sent him a physician to live with him...and keep an eye on him).
If he did accept the role, there's the added issue that this was not an era where generals taught complex tactical manoeuvres to other officers, they occasionally spread new tactical developments to them but largely left them to achieve certain goals by their own means. Additionally, most of Napoleon's military genius was devised around managing an army made up of huge numbers of levy recruits, whereas the British army was (and still is) designed on the basis of being a small unit but drilled and drilled and drilled to meticulous levels, and designed to fight enemies who have the numerical superiority. Mass recruiting wouldn't work in the British army.
Putting all that aside, there are a few things Napoleon could teach, I guess. The British had the slowest manoeuvring speed in Europe, as their regiment-level formation movements were based around the idea of deploying the entire regiment from column march into line abreast via one long "wheel" whereas most other countries deployed battalions (regiments were a British thing) company by company. This meant French battalions could get into line of battle I think about two minutes faster than the British. He would almost certainly advocate an 'ordre mixte' style which, given British superiority in firing to all rivals would be devastating, however at a far higher loss of life, not to mention that this again this really falls into the style of attack you use when you have regiments to spare, see above.
I know for sure he would also give his cavalry officers a mighty rollicking for the way that they had a tendency to get so caught up in the moment that, after carrying the field, sometimes they couldn't be reformed until they had chased a routed unit for more than ten miles, by which time they were so blown that they couldn't play any further part in a battle.
Im really not sure how much difference any of this would make though. The only thing, as you say, is that Napoleon would never be allowed to escape his house arrest to have his Hundred Days.
