How can I un-seize track nuts?
I would use the same techniques as used on rusted hardware. Liberally apply a penetrating oil (liquid wrench, PB Blaster, CRC Knocker Loose). Use a penetrating oil not a lubricant to break them loose. With the nuts being so small you can soak them in a small container for several days. Then hold the flange with pliers while turning the nut with a wrench.  Once it is freed up I would apply either Never-Seize or a dab of grease that will keep the water out and rust from forming.