RCOs are a bunch of xml files encrypted together, you can mod these with RCOMage and make custom strings on your xmb.
RAFs are Video files. the only one that is a raf is coldboot.raf, which is the boot logo. Can be made with ColdBoot Maker. Tutorial Here.
AC3s are of course audio files, which is the boot sound.
I might make a tutorial on modding RCOs for noobs if i receive some positive feedback.
1. put flash drive into computer and make the folder structure of customize/modz(example F:/customize/modz)
2. put all your customized files in that folder.
3. make sure all the names of the files are the same as the orginal(case sesitive)
• Minor message output changes
• Fixed bug where rcomage may have tried to convert non-GIM images through gimconv when dumping
• Fixed minor issue if Image/Sound/Text tree contained no subentries
• Removed option to select compression for PNG/JPG/TIF/GIF resources in GUI as it's mostly useless and may break the RCO if changed
• Add UMDFlag attribute to...