You are citing the conspiracy mythology about this case. Not what anyone alleges actually happened.
The fact that Oswald happened to work there before the trip was planned is really an argument against a conspiracy, not for one.
The motorcade route was published in the paper prior to the day, and Oswald read the paper. That's when he realized he had the opportunity. That's what it was, a crime of opportunity.
The route was not changed. Again, that's just part of the mythology.
Cannot be an “opportunity” when there are so many factors that had to come into play for a shooting to take place.
The top being removed from the car and security removed at the last minute are biggest clues to a conspiracy...
http://www.jfklancer.com/LNE/limo.html