I'm in zone 5b, north of Chicago, south of Milwaukee. I found bald cypress in pots need some protection from winter cold. Bald cypress are perfectly hardy in the ground. If I were you I would at least heal in the pots for the winter. That means, bury the pots of the trees in the ground, mulch over at least a couple inches. Or if you have an unheated garage, or a cold frame, or a window well. I use a well house to winter marginally hardy trees. Trees in nursery soils should be fine, as these nursery soils, though they hold a lot of water, are usually pretty coarse and open, usually based on composted bark.
I would NOT do any repotting at this time. For many years I would dig a trench on the north side of my house, line up the bonsai trees in the trench. Then fill the trench back in, lifting each tree so that the top rim of the pot is level or just a little below the soil level after I have filled the trench. Then a thin layer of an inch or two of leaves and then leave them alone until spring. Fine ceramic pots did not always survive this process. But plastic, mica & sturdy high fired ceramics came though this treatment just fine, as did the trees. I usually did not fill in the trench until after a few frosts. so I did not have much trouble with vermin eating the bark of the trees. Though my neighborhood always has a surplus of feral house cats, so mice and rabbits are not an issue.
Individual trees have different temperature to which their roots are hardy. The above ground part of the tree are hardy to one temperature, the roots are hardy to a different temperature. The ground stays significantly warmer than the air. In zone 5b your coldest average nighttime winter temperature will be -15 F or -26 C. If you measure temperature at 4 inches below the soil, roughly 10 cm below soil, your temperature may be as warm as +10 F, or -12 C. This is 25 degree F warmer ( 13 C warmer) than the ambient air temperature. Soil is an excellent insulator, and there is constant heat rising from beneath the earth. So healing in pots is quite effective. A cold frame is usually sunk below grade, so the bulk of its volume is underground, this is to get the heat from the soil. IF you use a cold frame. For most of the winter keep it covered with a layer of insulation, styrofoam wall board or other material. Glass does not keep the cold out as well as is needed for zone 5b winters.
Michael Hagedorn in his book "Bonsai Heresy" has a table that he uses which lists temperatures to which roots are hardy for a number of species of bonsai trees. The table was developed for the landscape industry. Because of copyright concerns I won't publish the table here, you really should buy the book, there are many excellent tips in there. It is well worth the $25 list price, and Stone Lantern often has deals, you might find it for less. As a result of his book I have begun to re-think my habit of wintering certain trees by just setting their pots on the ground, without any protection beyond that.
I have had success just setting pots of the ground of some trees in zone 5b. For example, eastern hemlock, Tsuga canadensis, all my spruce, Picea, and Pinus strobus, sylvestris, mugo, and P. ponderosa, all just get set on the ground. Also junipers. But I do protect by moving to my well house, azalea, bald cypress, ginkgo, and many other less root hardy species.