At first I didn't. But now I have changed the actual name of the html files and the references to them in the toc.ncx. Now I am getting an error with the epub validator
ERROR: E:\zzzzzzzz F23 use to edit\F28Hyphen.epub/OEBPS/toc.ncx(2753): 'OEBPS/My-book-05-21st-Oct-2012-457.html': referenced resource exists, but not declared in the OPF file
Now I've opened the OPF to take a look. Near the top of the doc I see a list of references that look like this:
<item id="My-book-05-21st-Oct-2012-381" href="My%20book%2005%2021st%20Oct%202012-381.html" media-type="application/xhtml+xml"/>
and further down loads of these
So it seems like the revised name is declared in the OPF but the validator is saying it isn't. So I don't know what it is I should be changing.