Yes. For an example, compare the underlying XML of http://globestroller.com/maps/US_48.svg with the original at http://upload.wikimedia.org/wikipedia/commons/e/e9/Blank_US_...

In the original the states already had IDs (except, for some reason, Virginia), so it was simply a matter of moving the inline styling to a CSS section at the top.

The CSS can also be in a different file, which could be dynamically generated for different users if you wanted to build a simple "make a pretty map of which states you've visisted" app.