I would definitely stay committed to the 4H formost as it seems like that committment was made first, and if time allowed after the 4H competion, attend the Jamboree. To work so hard to get to where he is with the 4H and then set it aside with coming and goings definitely sounds hectic and undisciplined, besides wouldnt be a good lesson for him to learn about committments and finishing up something once you have started. The Jamboree, if I am remembering correctly, is really just an introduction to the football season and doesnt really hold any weight as to what place the team will stand in by the end of season, right?
My son use to love his sports, played them all and the seasons would overlap from the end of one to the beginning of the other and I would not allow him to sacrifice the first sport he was already committed to to begin a committment with another team, also letting the coaches know right away about the prior committment and following through on that first. At the time, my son thought I was being "uncool" all his friends were aloud to pick for themselves what they wanted to do, but guess what? All of his friends went from colleges to Universities, from state to state, (which I absolutely refused to allow him to do as I was paying for his education) and not one of his friends completed their studies, returned home no better than when they left for college. My son? He completed 5 yrs of schooling at one college and walked away with a double major! Today, he is thanking me for being so "uncool", not only is his working in the profession that he studied for making the money he dreamed about, he is also one of the junior coaches for the high school team he once played for. As for his friends? They are watching him coach!