What if someone by mistake wrongly connect the load on the switch (L) to one of the other wires (yellow, red, green)? Can this (cross wiring or mixing) cause (cross-wire) damage to the motor? Please help. I need this help urgently.

Green is ground. Connect it to load, and the breaker trips if you are lucky. I bet yellow is low, red is medium, and the switch connects both for high. Mix up red and yellow, and you go from off to medium, to low, to high. Shouldn't hurt a thing. To make a more logical world, if you do mix them up, switch them.