I believe I've found a bug (or at least a design oversight) within Lightroom 5 Publish Services (Hard Drive):
I've created a Publish Connection that uses the 'Copy name' token in the file renaming scheme. However, I've found that if I change an image's copy name, and 'Mark to Republish', it won't use the updated copy name. It seems once an image is published within a Publish Connection, its export filename is forever locked. The only solution I've found is to delete & recreate the Publish Folder.
OS X 10.9.4