@lostnbronx No need to change the name of an epub to unzip. Just do
unzip blah.epub
and you'll be left with the mimetype, META-INF, and OEBPS dir.
The inverse of that is actually how I make my epubs. Zip the mimetype up with 0 compression, and then zip the other stuff with max compression. Simple, and no need for any big, special "epub generators".