On the other hand, ...
One can "slip-pot" any potted plant at any time one wishes. "Slip-potting" is simply taking the intact soil and root mass from one pot and placing it into another larger pot (and adding the extra soil, of course).
As I understand, the problem created in otherwise-repotting is that the root damage reduces the water intake capability. If one were to reduce the transpiration rate by defoliating, one wouldn't have a water loss problem. Deciduous trees will routinely generate a second set of leaves. IIRC, Tridents are noted for being capable of sustaining at least two defoliations in a growing season.
Another factoid is that deciduous trees are often propagated by cuttings taken after the leaves are hardened. The struck cuttings are misted to keep the cutting hydrated and the process of generating carbohydrates running until sufficient rooting has occurred to support the new tree.
So, if this is the correct science, one ought to be able to procede with some root reduction, if one were to also at least partially defoliate the tree. If leaves are wilting after a few days (even withkeeping the repotted tree in a shady place), one could make a little plastic tent for it, to hold in atmospheric moisture. IMHO, one would also put in a wad of damp sphagnum or a damp sponge to act as a moisture source. Once the remaining leaves have perked up for a week or so, the tent can be removed.
Since you have several new trees, why don't you try to learn something from them? Like, leave one or more untouched or slip pot them. Maybe reduce the root depth one or more as Mach5 (reluctantly?) suggests. And I encourage you to be brave an risk losing at least one by partially defoliating, combing out the roots from the soil they are in, and truely repot it into new soil. Then compare the health of the trees thru this growing season.
IMHO, the fun part of bonsai is learning what can be done. Some wise bonsai enthusiasts have said things to the effect that doing bonsai means killing a few trees. Be brave and enjoy!
