I think the pertinent question here is not "can the civil war be changed to butterfly Booth" so much as "can Lincoln be convinced to be less cavalier about his own safety, so more careful precautions are taken to protect him?". It's true that before then no US president had been assassinated but I do recall him being urged to pay more attention to his own security, so perhaps if one of the failed plots against him is more of a near-miss and he finds out about it or if Booth's plot is uncovered at the last minute it might force him to admit he needs better security.