Never fertiilize before super hot weather. If your plant is not drooping, the ST or B1 will just help promote root growth. Use just a drop or two in a gallon and water. Wait for cooler weather to fertilize. ST is hormones not fertilize so not a problem. If your plant was dormant, transplanting without water is ok but not the best as you need to keep the roots from shock of exposure when removed from the pot. At any rate, your plant should not be dry going into hot weather. You may want to give partial shade or put a cardboard paper towel roll or aluminum foil around the stem to prevent sunburn.

Thank you for the info. My plant was actually not dormant. I've had it in and out to wake up, and it actually already has some great looking leaves-- it's been in full sun for a couple of weeks now but I have been bringing it inside when the temperatures dip-- so you think I should add some super thrive and water??

It should be fine either with or without Super Thrive and should adjust quickly to being repotted. Since your cactus mix should be pretty well draining I would say just like any other time, water it thoroughly and then don't water it again until it dries out a bit. It should be just fine, keep us updated on your progress!