She said "...told that the parties would be an exception to some of the guidelines and more clearly defined guidelines would come at a later date.." which really was very vague and could mean anything or nothing. I've asked a MK CM manager friend and right now, they know nothing about what the rules will be but right now no one over 14 can wear a costume IN the parks.
Pkltm only mentioned MNSSHP. But I don't see the connect here, especially since backstage in costume would likely be a bigger problem than in the parks ... and they allowed it with guidelines.
NOW in reference to RunDisney, rules were loosened and guests were allowed to wear costumes with guidelines DURING the races but were instructed to remove them before entering the parks after they were done the race.
To my knowledge, they've never gone on sale as late as June. They typically go on sale at the beginning of May, but last year it was April 8. Unfortunately, you can't rely on what phone CMs tell you.