add length to the vest?

My nearly 9 year old measures size 8 in the chest, but is 58" tall - the tallest that a size 12 accommodates. I'm thinking of a size 10 (for room to grow) but with extra length so he can wear this for more than one year. It seems I should add the length at the side notches and reconnect the darts. However, this will impact button spacing. So should I do this and re- space out all the buttons?