General Narciso Lopez tried to invade and liberate Cuba from Spain in otl. Twice. He failed both times but his martyrdom inspired many mercenaries to head into Central America causing quite a few problems for a while. According to wikipedia he also tried recruiting future CSA President Jefferson Davis and General Robert Lee to join his army. Obviously they didnt in otl.
But lets say they did, and manage to survive. I still dont think the invasion of Cuba would succeed, but for the purpose of rule of cool lets say that after the failure of Lopez's Second Expedition, Lee and Davis form their own mercenary army afterwords and attempt to go filibustering against some poor Central American nation afterwords.
How successful do you think they would be?
Maybe instead of William Walker, Jefferson Davis becomes President of Nicaragua? Or maybe they leave Walker alone and try to invade somewhere else.
Or would they fail horribly and be put to death by the USA/return to the United States defeated but hailed as heroes?
Yeah this whole thing's basically trying to run on rule of cool.