Challenge: Have Napoleon lose the war, but instead of restoring the Bourbons back to the French throne, have the House of Bonaparte remain the emperor.
One possibility is to have Napoleon's son, who's mother was Austrian, Napoleon II become Emperor, with someone was regent until he was old enough, since he was at least 3 year old at the time.
OR
Challenge: Have Napoleon III remain in power, after the Franco-Prussian War.
One possibility, is Napoleon III isn't capture, and makes a peace, and wins the fight against any revolutionaries that rises up.
One possibility is to have Napoleon's son, who's mother was Austrian, Napoleon II become Emperor, with someone was regent until he was old enough, since he was at least 3 year old at the time.
OR
Challenge: Have Napoleon III remain in power, after the Franco-Prussian War.
One possibility, is Napoleon III isn't capture, and makes a peace, and wins the fight against any revolutionaries that rises up.