I'll just carry the old red one in the trunk. In fact, I do carry a spare rotor/cap in there anyway. If I paint it and the car runs like crap, I'll just switch in the other one. Chances are though that it will be because I put the wires back on wrong. I don't know how many times over the last three decades I've done that -- even on four cylinder cars. For some reason, it's like my mind turns off mid-way between switching over the wires.
