Fun fact, the credits for JAD2.21 are randomly selected from 11 different songs! (If you didn't notice, either you got the same song twice or... only played it once...)
During the main campaign, there are some sort of cheat codes
that allow you to force the ending song to a specific one. Basically press the button in brackets before the credit song starts.
You can also download this mission: http://lazymodders.fsmods.net/releases/missions/jad222-credits.rar
(Goes in your JAD2-2/data/missions folder. Make the folders if they aren't there)
With that you can just fly through the song you want to see played. Not only that, but you can also select your own custom song!
Here's what you need to do this.
Get a song, the credits are timed to be around 90 seconds long (most anime EDs are that length).
Convert it to ogg or... wav.... There are a ton of free converters out there! MP3 won't work!
Name the file jad222-customED
Put your converted file in your JAD2-2/data/music folder. Again make it if it doesn't exist.
Play the mission and fly through the jad222-customED ring and listen to your own cool version!
As well you can destroy some containers in the mission to turn off the credit text (giving you a clean ED) or silencing Holley's commentary during the credits (giving you an even cleaner ED).