1. I am not sure about this one.
2. Do you mean like switching them and putting the other one into the same socket? If yes then if it's the same socket cpu then it should work fine.
3. You mean taking apart a computer and using the parts in another one, then if all the parts are compatible then there is no problem. As to laws there is nothing stopping you from taking a computer apart.
CPU - AMD Athlon II X3 450, MB - Asus M5A78L-M LX, GPU - EVGA GTX 660 Ti, RAM - 8GB Ballistix 1333Mhz, PSU - 600W OCZ Modxstream-Pro