Check the rules of your contest, but from what you said, it is probably okay? I have never known anybody to care if you are going up a category, especially if you are adding things. The question I have is the relative size of the conventions. If the May one is smaller, you are almost definitely fine. If the May one is bigger....maybe? You're still going up a category, so probably okay, unless your July con is drastically smaller. Do check the rules though, some contests only want new costumes.
In Progress: Madame Red 2.0 (Kuroshitsuji plus some extra historical fashion influence)
Female Ranma (wig only) Ranma 1/2
Anime Expo 2016