Regardless. If the tree is green, healthy, and growing extensions, it means it is doing really well, and it is well established in the pot. Re-potting and styling at the same time shouldn't be such big problem for the tree. Unless you chop too many roots, or eliminate too much of the foliage. If you go from a 5 gal nursery container to a half an inch deep bonsai pot well... you are asking for trouble. But if you remove 1/3 of the root mass, and go to 3 gal nursery container or similar, and re-style. If the tree is healthy, it should not die. I've experienced this myself when I was starting on the hobby, I took a healthy Juniper from a 5 gal pot, re-potted straight to a deepish bonsai pot, I removed a little more than 1/3 of the roots, did structural pruning, and even absurdly extensive Shari. The tree survived, not 1 branch died, and it is growing as well as Junipers I left untouched.
Of course it doesn't look good, and the shari is ugly as hell and done wrong. But with all that drastic change, and the tree recovering, tells you a healthy juniper can recover from mostly anything. My extreme case must have involved some luck as well. But getting to the point, if you only remove 1/3 of the root mass, cut the right roots, keep the roots moist at all times so they don't dry, and style the tree; doing all this at the right time of the year. It should recover no problem.
You are probably more likely to kill the juniper if you remove way too much foliage.