Didn't you panic about your honey locusts earlier? And they're still alive!

So, don't panic too early. The spruce will likely fare better in the cooler room, yes. Not sure about the shock, can't translate F to °C in my head. 🤔 If it is in the minus degrees in C, the transition needs to be slower. (Those cold climate trees do fine in my area, where some winters it doesn't get below -2 or -3 °Celsius, and likely would also survive the occasional winter without frost, too - I suspect it is more the extreme heat and dryness in summer that harms them.)

Don't worry too much about having messed it up. It'll just feel like an unusually warm winter. That does make trees more susceptible to bugs (or is it just that the bugs survive better with warm winters?) but your seedling is young and healthy and too small to be a target for anything larger than aphids.

If you had the plant lights on all day, cut that down to natural daylight hours for this time of year. Daylight hours is an important signal for plants, too.

I usually take a "as long as it is green, it is fine" approach to gardening (which is likely while I fail so often, but ... I'm not always wrong!)

I would transfer them gradually, moving houseplants in and out of doors has always been a tricky thing for me. Previously thriving plants hate me after the switch. So what I've learned is, start them out on maybe like 8 hours a day in the cold room, then increase, so they can get used to it.

I would put them in your back room for the winter. It’s possible they are going dormant anyway.

If you live in the north, your Gleditsias' genetics may be making them go dormant anyway. The low light provided by the most common "grow lights" may simulate the reducing light of autumn.

https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/gleditsia/triacanthos.htm

Your little spruce also needs plenty of light. I would take it off the heat too, as it doesn't need it. If you slowly acclimate it (like set it outside in the middle of the day for an hour, then two, etc) and protect it from freezing temps (plants in pots really suffer in those conditions) then it will grow slowly but should be fine.

I feel ya on the plant babies: I just dug up a whole bunch of freshly-sprouted sugarberry, green ash, persimmon, and trumpet creeper a couple months ago. And yeah, I'm fretting over them. Mine are outside in a greenhouse, but we just had a wave of hard cold.