Hi,
There's no method through the GUI that I know. If you really have a lot of stuff, you could do it through SQL:
umpQoSReports table contains the actual reports.
PortletPreferences table contains the preferences for each portal.
The bad news is, that the column you want to edit is in XML, like this:
<portlet-preferences><preference><name>report</name><value>test</value></preference></portlet-preferences>
So what you'd need to do is modify you "path" in umpQoSeports table, and then modify the "preferences" in PortletPreferences so that the report name contains the new name.
-jon