No.If French support makes it so that the war is still being fought by 1866, I wonder if the Chassepot rifle could be supplied to the CSA in any substantial numbers? The next question would be is if that would be any kind of significant help?
Rifles did not win the war. Money, productivity, and men won the war.
The crappy American tanks of WWII bested the amazing tanks of the nazi's Because no matter how many of our crappy tanks the panzers took out- we still have even MORE tanks on the front the very next day.
Modern war is not decided by weapons.
Its Potlatch. Its always a contest of economies and populations. Whoever has the greater ability, and WILL, to throw away materiel and men and still keep fighting ALWAYS wins.
Napoleon was doomed- because the alliances against him- combined- had the material wealth to just keep coming at him until attrition left him unable to contest further.
The North had four times the population- with ten times the industrial wealth- Shelby Foote famously wrote that the North fought the war with one hand behind its back. That at no time did the costs of the War significantly impact the economy or population of the North. As long as they had the WILL to hold the union together- they had the power to hold the union together.
No fancy rifle could have changed that equation.
War is not heroism. Its not even tactics. You can lose every battle and still win a war.
War is profligacy.