Sorry I should have been more specific.
Rune magic is from the Forgotten Realms Campaign Setting book. It allows you to create runes that do various effects.
In it, it says you can place a rune on any medium object, but only one. Didn't say anything about applying a rune to and already...
Don't forget you might smell because of being all decaying and people might not like you. Should wear some perfume or eat some garlic and eating also helps keep up appearances incase they don't notice your eyes and skin and deadly magic.