How can I change three hundred procedures at once?
If you script the procedures out to a file, the search/replace can be trivially dome with a sed script along the lines of 

s/\/file\/folder\/documents/directory_name/g


(note not tested, just off the top of my head, but you can fiddle with it).

Then you can re-load the stored procedures.  Note that if you're frigging with the code base you should really test what you're doing rather than doing a blind search/replace on production code.  What could possibly go wrong?