Napoleon was by education a reasonably "technical" person but there was very little in the terms of the new military technology in his army. What can
realistically be done to make things
noticeably different?
"Realistically" means something that was invented/introduced in OTL within a couple decades after Nappy's reign or things that had been introduced slightly later but did not require technology seriously different from one available in Napoleonic times.
"Noticeably different" - giving a clear advantage over the opponents. Preferably something that would not be easy to pick up immediately (just due to an absence of the technical information).
Some of the candidates:
1. Paixians naval gun capable of shooting big caliber bombs on flat trajectory - in OTL developed in 1822–1823 in France and introduced in the French Navy in 1830's. The main calibers 80 and 30 pounds (bombs). In the 1840's similar guns were adopted in the British, Russian and American navies. The 1st naval battle (there were earlier deployments on a lesser scale) test at Sinop (1853) proved to be quite effective. With few "bombing cannons" (out of a total of approximately 700) the Russians sunk and burned practically the whole Ottoman squadron and destroyed the coastal batteries. Explosion of a bomb in a side of a wooden ship was producing a hole approximately 1 sq. meter so at the distance of 500 - 100 meters a ship could be sunk with 20 - 25 hits. Explosion inside the ship would be causing serious fires. Quite different from the protracted naval duels lasting for many hours. Could Trafalgar be different with enough such guns being available on the French side?
2. The percussion cap for muskets - in OTL introduced in 1820's as a substitution to the flintlock ignition system. Even the first models were less prone to the misfiring (especially in a wet weather) than the flintlocks and the existing flintlock muskets had been easily converted. As I understand, the rate of fire was at least somewhat improved.
3. 12 pounder "Napoleon" field howitzer (wrong "Napoleon"

). Seems to be very popular and effective and, being a smoothbore, well within the technological level of Napoleon's time. They had been lighter that 12 pounders of the "System of Year XI" (1,227 vs 1,530 pounds) and could fire solid shot,
shell, canister or
grapeshot (in Napoleonic army only howitzers were firing shells). Effective range was up to 1,619 yards while the same of the Napoleonic 8 pounders was approximately 900 meters.
4. Steamships. Robert Fulton was working in France between 1797 and 1804 (and designed the 1st working screw-propelled submarine) and his 1st paddle-propelled steamboat was built in 1806. What if he continued working in France and built a screw-propelled steamboat? The timing is post-Trafalgar but what if it moved couple years back? How/if even few steam ships (even paddle-driven) armed with the Paixians naval guns change a naval situation? The Brits still have a LOT of ships but wouldn't they be quite vulnerable? (Assuming that it would take Brits at least couple years to pick up with the trend).