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That doesn't sound right? How come it still has leaves? It should be dormant now, without leaves, and not under grow lights.
I guess that's -25 in F? That's -3,8 in C. Trident maples can handle that easily (hardiness zone 5-8 ).

But I'm confused. Did you keep them inside all winter ?

Tridents should be repotted in early spring, but if your tree hasn't gone dormant, I don't think I would do that now.
What's the reason for repotting? I understood your idea was not to separate and re-arrange them?

The time to repot just about any deciduous tree is right before the buds break open in spring. So why the buds start to swell and you see the green lines starting to appear on them, that is the time.