Please post your custom Ps3 Boot Logos here!
You can make new Logos with this Tutorial (Tutorial: Custom PS3 Boot Logos)
To replace the original coldboot.raf file with a custom one you need to write to the flash. To do this, you can use the new "Dev_Blind v1.0 for PS3" (not tested) or start the AsbestOS-installer once (it will fail) and then you can replace the original file (after a backup) with the new custom one (using any filemanager - i used multiman) in dev_flash\vsh\resource.
No warranty that your PS3 won't brick when doing this. But mine didn't.