Felt pen can sometimes be removed with alcohol.

Melissa, I talked with a luthier yesterday who has used automotive lacquer on his dulcimers. He said it works very well, except that sometimes it doesn't! Occasionally, after a while, it 'crazes,' shows a pattern of surface cracking that makes it look old. Perhaps atmospheric conditions when it was applied, perhaps how much was applied? Perhaps the larger areas on a guitar might make it more prone to cracking?
Perhaps crazing might suit your purposes better, making it look older faster?
We also discussed this thread, He thought Shellac might suit you. This is (waxy, chitinous) beetle wingcases dissolved in alcohol and painted on. If you rub it on lots of times, it is called French Polishing. Same stuff, different application system. Chris.