The main risk is that your tree will use so little water in fall, that the roots quite litterally, drown in water. If you can shelter it during heavy rains, it should be OK.
I have styled most of my junipers in winter.
I'm not considering root-pruning before next Spring, when I'll re-pot it. I'd just like to remove some branches that know I won't keep, like lower ones and young shoots in wrong places. It's also tempting to shorten some longer branches, but I can wait if that will be too stressful.
What I'm really asking is how resilient junipers are to branch pruning. Can it be too stressful if I do it during the Summer?