it needs quite some coding, you can use this override to create 'site.com/projects' pages with same content as "tags" page:
$routing = qa_page_routing_base();
$routing['projects'] = $routing['tags'];
what remains is: 1)completely removing Tags page or redirecting it to new page and 2)replacing link in navigation. both are easy so I won't go on any more.
*** there might be easier ways which I'm not aware of. if so, please share.