My guitar seems to get taller when it's cold. . .

This is the characteristic of the needle column, which expands with heat and contracts with cold, and the string hardens, which is normal. It is recommended to put the guitar in a warm environment. After all, being too cold and too dry will cause the acoustic guitar to deform or even crack, and the timbre of the guitar will be greatly reduced.

Ps: It seems that you are a fan of beyond. Hehehe, I studied beyond songs for several years before. Let's discuss it sometime.