Could I take out the parts of a Mac mini and put in new ones?

The major problem would be finding components small enough to fit the Mini case. Then they would also have to be extremely low powered so as not to overheat in use. You would certainly need to use an external power supply and you would need to check with hackintosh forums for parts that will work with Mac software. So I guess the answer is yes its possible but not practical. If you decide to go ahead with this project keep good notes and pictures so you can post your results on a Hackintosh forum.