Yes, that. You can use any text editor to fix the completed cobra.csv script (Notepad will do for Windows, TextEdit for Mac) - just be sure to keep the .csv file extension. When renaming the .mp3 file, be aware that Windows has a setting "Hide extension for known file types" that you can set in Explorer; it is ON by default, so a file "xxx.mp3" looks like just "xxx". The problem comes when people rename their file and add the ".mp3" meaning they just renamed the file from "xxx.mp3" to "yyy.mp3.mp3" which of course doesn't work correctly. Personally, on every Windows computer, I start Explorer and get into the view preferences, and uncheck that "Hide extension" option.
If you're still working on your script with Cobra Show Creator, just rename the audio file and then when you start CSC it will tell you it can't find the audio file and prompt you to find it. You then just navigate to the file and select it. That will I believe update the .csm show file and then when you export (or re-export) the cobra.csv script file it will be correct.
For testing purposes, I always keep a pair of cheap headphones with my Audiobox so I can start the script on my 18R2 and hear when the music begins.