Won't happen for obvious legal reasons... And topics about Arcade maps are not really appreciated on the forum for the very same reasons.... Moreover costume changes ? You know the background movies you see during gameplay are movies ... actual mp4/avi files, you can't alter them to change costume. You can replace them by other movie files with different costumes if you like but that's it.
So yeah it's a taboo subject. With that said I think you can find what you wish for with a few google research maybe try "PPD Arcade Version" for instance, or "PPD JohnnyKLawliet" .... Just saying
That's the very same reason you have the website doesn't provide a direct link to download video/songs. Legal stuff
About the source code ... I don't think it's a good idea to go open-source as KHCMaster maintains the game all alone on his free time. And I think there is not enough developer around here to maintain the game open source and secure. Cause if it goes open source, anyone with basic programming skill would be able to upload fake scores and boost their account.... But I do think KHC needs to find someone to help him ( *wave at his direction* I might help you on that ), someone he can trust.
A wild non japanese player appears !