Britain's might in the 19th century was predicated on its naval power. The French Navy, while no slouch in conflicts like the Crimean War, was a distant second or third when it came to the number of vessels.
Without significantly diminishing size of the British fleet, is it plausible to get the French naval fleet to parity with that of the British Empire's by the time January 1st, 1900 rolls around? I'm guessing that run-up would affect France's performance against Prussia in 1870, but do the necessary changes have to start before the future Napoleon III become president in 1848 of the Second Republic? How far back would the PoD need to be plausible rather than ASB?