Can a bicycle frame undergo a physical change?

Yes, bicycle frames can undergo physical change. When metal bike frames get warm, the expand a little bit. It's not much, but they do, and this change is a physical one. All bike frames warm up just a little bit when we ride them. The frames flex just a tiny bit when we apply the stress of riding to them, and they will respond to the flexing by warning up, and the increases in temperature will cause the material to expand just a little bit. In metal frames, the metallic properties of the material from which the frame is made will undergo changes. Metals that flex or move while in use undergo what is called work hardening. The metallic crystal structure changes and smaller crystals form out of larger ones, and the metal becomes brittle. This is just one form of physical change that a bike frame can undergo.
A physical change of a bike from would be if it is bent or cut.