Automate renaming files within zip archive

I have a large number of files where I need to do the following:

• Change the file extension to .zip. (The files are zip archives but with a special extension, and all of the files have their own extension, ie .xx01, .xx02, etc...)
• Extract the zip file.
• Rename a file within. (Alternatively, it'd be great to be able to rename the file without extracting the zip file.)
• Recompress the file.
• Set the file extension back to what it was.

I've been playing around in Automator to see if I could create a workflow that would do some or all of this. I've figured out changing the file extension, and Automator has an action to compress a zip file, but the other parts are eluding me.

Does anyone know a way to make this process a little less labor intensive? I'd prefer to automate the whole thing, but even just some way to rename a file in a .zip archive without extracting it first would be hugely helpful. (I know this is possible under Windows.)

I'm comfortable with delving into new territory in Automator, AppleScript, or shell scripts to make this easier.

Thanks!