Shame Napoleon never tried to liberate peasants/serfs in OTL invasion of Russia
Well, in any case it would never have worked.
Firstly, Napoleon would not have been able to conquer enough of Russia fast enough to offset the mobilization; Russia was capable of mobilizing more soldiers in a war of national defense than had the Grande Armee; given time they would have outnumbered Napoleon by hundreds of thousands. Secondly, turning this war into an existential one for the Russian nobility was the exact opposite of what Napoleon should have done; even assuming it would have worked it would have been a long and painful effort of nation-building, and after beating the nobility in a brutal war of attrition. Finally I'm not at all convinced the peasants would have bought it; no one likes armed missionaries, as Robespierre said, and the serfs were likely to care far less about abstract concepts like freedom than they would have about the foreigners with guns demanding food; live off the land had been the French strategy for 2 decades at this point, so unless Napoleon wanted to build an entire logistical support system from scratch he was going to need to take food from the peasants he was supposedly going to be liberating. War on the Chateau hadn't worked in the War of the First Coalition and it wasn't going to work now. You cannot invade a country without hurting the civilian population no matter what you want to liberate them from.