Yes, you can easily clear coat over artwork if done correctly. Compatibility will depend on the type of marker/clear coat combination you use (some clear can "melt" weak marker ink causing it to run). Your best bet is to use a 2K poly clear (such as the 2K Clear Glamour by SprayMax) but take the safety precautions seriously! I'm not sure what kind of art pens work best (ask Joe!

). Ideally you would first lightly scuff sand the entire body (this creates a better mechanical bond b/t old and new clear coats), wipe down with a weak solvent (like naphtha), do your art, then begin applying the new clear coat. First pass should be a very light mist to lock in the art, after this dries you can continue with light-medium wet coats until you build up an acceptable thickness (up to you). This is the general approach...you could also hand off to a luthier.
The only thing I would caution is make sure you want to do this! I don't know about you, but my tastes (and talent) at drawing changes all the time. Depending on how good you are at art and finishing, you could easily end up with something less than satisfying. Why not do a complete refinish? Pick a great color you like (maybe with a little reflective flake in it), have the local auto paint shop mix it up and put in a rattle can for you, apply, then finish with clear. Just an option, good luck!