[RonF]

True. He was a special exception passed by Congress in some fashion, probably due to the fact that he was killed in office, something that Reagan almost fell victim to, but avoided.

[Conservative til I die]

Not sure about paper money, but with coinage, the way it works is that designs can only be changed every x years (I think it's 25) without legislation. However, you could change the design of coinage every six months theoretically (ignoring the pointlessness of it) as long as you took a vote to change it. Living people have occasionally appeared on US coinage, albeit only commemorative coinage. One of the Shrivers was on some sort of Special Olympics commemorative coinage. PT Barnum was ona commemorative coin too, but I'm not totally sure if he was dead or alive at the time the coin came out.