Can you just literally lift the whole thing out of its pot in one piece, very gently bring down the worst of the 'up' roots, and get it into a slightly larger pot just tamping new fast draining soil around the rootball for now and doing nothing else at all til spring? Best to wait til Oct/Nov. even for that though.

We had a storm that broke some of my bonsai pots so I had to repot them in the worst of summer. So far so good, I haven't lot one yet. Zack

As long as you're not cutting roots it would be OK with the proper recover period and method. Keep them out of full sun for about a month. I had to repot a failing san jose juniper about 6 weeks ago in 100 degree heat and it has put out lots of new growth.

Repotting seems to be something many people fear. If the mix you have your tree in is too rich (think dirt) then the drainage will complicate things further than an out of season repot would. Thats not to say that repotting SHOULD be done at any time, but it can be used as an emergency fix. The sooner its in better soil (with good aftercare including proper watering technique) the better the chance of survival.

WF

I just repotted my Chinese Elm which is in a very tiny pot and the summer here is very hot. I just lifted it out of its pot like mentioned before and inserted it into a bigger pot with gritty soil all around the base. Time will tell but I cannot see how this could drastically affect the tree when nothing was really upset much.