The rivets are there to hold the assembly together at the factory.
To get the rotors off, you will need to drill the rivets out. You do not need to put rivet back in, the wheel lugnuts will hold the rotor on.
You will need to replace the rivets only if you are going for an NCRS judging, they will count off points for missing rivets, but mechanically, you do not need them.
BTW, Welcome to DC!