The official Disney website doesn't show a course map or if it does, wasn't obvious to me where to find it. Seems like basic info the participants would want to know............LOL. The only course map I could find for both the upcoming 5K & 10K races were not official Disney sites so not sure how accurate they are. I prefer official Disney sites to various 3rd parties since they tend to be more accurate.
Both events go through part of Epcot. MK doesn't seem to be involved. I would imagine that while the race is underway, part of Epcot might be blocked off or you would find a lot of spectators standing around. The biggest inconvenience is how it might impact transportation or if any roads will be blocked.
Might be a good time to do MK if the race is taking place at Epcot. Or check the race info to see when those 2 races start/end or if they are on the same day. Barricades would likely be removed once the event has ended.
A few years ago we happened to be at Disney when one of those cheer competitions was underway. We never noticed any difference at the parks since the contestants were busy during the day either practicing or participating in the competition which was taking place somewhere else on the property.