Nop, adding the xwbar.lst in the remaster doesn't do anything. I tested by removing everything but the exittc entry from TC's default ~/.wbar config and copying it over to /cde/xwbar.lst. Rebuilt my remaster and booted up, and it still shows the default TC bar.
EDIT: So adding a /home/tc/.wbar in your remaster DOES work because on bootup, TC will fail to run the symlink cmd (ln -s) to link tce.icons to ~/.wbar (you will see ".wbar already exists" errors upon booting up). Not sure what I was doing wrong before. Anyway, I'm sure this is not the cleanest way to do it, but I guess it works for now. Still, what is the proper way to do this?