We know the chances of a sealion is seen, by pretty much everyone, as zilch, both in the Napoleonic Era and in WW2 (though I see the WW2 one as Hitler trying to scare the British into suing for peace than not actually attempting an Operation Sealion). However, I recently read in a thread that France's navy was at least on par with the Royal Navy up until the Revolution due to the Navy being filled with actual royalists or suspected Royalists, seeing many experienced officers in the navy be purged and executed for "betraying the revolution". So the challenge here is, without causing too many butterflies that it prevents the rise of Napoleon, keep the French navy strong, experienced, and capable enough to conduct an Operation Sealion under the Little Corporal in 1805. From there, you can discuss how a Napoleonic Sealion would go (and maybe how Egypt and Trafalgar could be different due to a better French Navy than OTL).