In our farm we have several features that add extra themes. These features automatically update the spthemes.xml file in the template\layouts\LCID directory on activation (and remove the lines on deactivation) All the 'file updating magic' happens in the feature-activated event receiver.
Same for the pdficon in the docicon.xml file.
We just added a new WFE to the farm, but the changes aren't replicated to the files (docicon.xml and spthemes.xml) on the new server.
What is the best approach to keep these kind of files in sync when adding a new WFE?