Here's a real answer:
Effects like that would be very minute, but potentially build up. Alternate history, I have found, is realistically a future history from the set POD, with fore knowledge of what really happened to understand how things could have gone. Living in the moment, as all reality is living in the moment, so many things could have gone differently within the framework of Lee Harvey Oswald planning to kill the president, and going to that floor and that window and aiming his rifle and shooting. Taking into account a change in history before, you could be assured that things would have gone a bit differently. If you replayed events over and over things would be slightly different because no one plans out every exact thing; we plan out overall things and try to make them work and happen, but the factor of living in the moment and living from moment to moment is never and couldn't be planned out and would always be different on every play through of time. Taking that into account, Oswald could fire later or sooner, or aim different areas or possibly try to target more people, and his actions thereafter would be randomly different in the overall idea of "I have to get out of here" that he had. And things would build up from there like grains of sand on a beach, each grain being all the tiny little details that build up an and action and event. And history thereafter would have it own random differences for all the reasons I outlined before.
The short answer is, history would be mostly the same, then possibly different as time goes on as every playthrough of history would have differences and they build up over time. So we have no clue.