There is a set in Portage to rebuild modules, @module-rebuild; therefore sys-kernel/module-rebuild has became deprecated and is planned to be treecleaned.
fixed in CVS; thanks for reporting. also fixed nvidia-guide.xml. i assume there's no need for the "module-rebuild populate" function; that portage keeps track of all this automatically, and the only thing users need to do is run "emerge @module-rebuild" -- if there are any other steps, please let us know.