Vliger2002 I Just remembered and checked and the answer is yes you can boot apples FW without a alternate bootloader.
When apple logo appears, hold play and it will go to apple firmwareWith the new iPod bootloader you (re)boot and immediately toggle the "Hold" switch to the on position to boot AppleOS.
The basic install and builds are stable and almost 99% non lethal if you screw up.Rockbox, official or not, is 100% non-lethal if you screw up.
You will only boot Rockbox after a full shut down (Hold Menu and Select for a few seconds)Not to nitpick, but "Menu"+"Select" is not a shutdown command, it is a reset command. While it is true that you must perform a hard reset to get out of AppleOS (unless you are willing to wait two days for AppleOS to go from "Sleep" to "Power Off") propagating the misconception that it is a shutdown leads many to falsely believe they have cleanly shut down their player when, in fact, they have done the equivalent of pulling the power plug on their computer. Rockbox will not save state when you reset it so abruptly.