You could look at the Excel shape's to create your own. SourceFullname attribute of links. It will direct you to the place where PPT anticipates finding the file.
The file can be changed by moving it to the desired location. LinkFormatSourcefullname points to the updated file's full path. Relative paths won't work; they must be the complete path.
If the old path and the new path are consistent, there is some VBA code to automate this here:
Batch Search and Replace for Hyperlinks, OLE links, movie links and sound links http://www.pptfaq.com/FAQ00773_Batch_Search_and_Replace_for_Hyperlinks-_OLE_links-_movie_links_and_sound_links.htm