Two weeks back I decided to have a go at shaving a few seconds of my AmigaONE 500's boot time. I did this by editing the the 'Kicklayout' file, a file which determines what kickstart modules are loaded at boot. I knew this process was hazardous, possibly resulting in the machine failing to boot if the wrong line was commented out, however having done this on my old Sam440flex I decided to have a go.

Evidently I got a bit carried away and commented out the crucial PCIGraphics module by mistake. This one misplaced semicolon resulted in many hours struggling to get the AmigaONE to boot properly again. I thought I could boot from my backup disk and remove the offending semicolon, however I had forgotten to make the CD bootable! I then tried making my backup disk bootable on Windows. I didn't manage to make a worker disc although now have a selection of shiny coasters.
I next tried the AmigaOS 4.1 Update 2 CD and the SD card that came with the system. I struggled to get anything useful done with either of these, with various USB mice and keyboards not working properly because of Update's 2 older USB stack. Strangely no programs seemed to want to load from the AmigaOS CD, i.e. NotePad or Shell. Oddly the system seemed to lock up when trying to copy a file from one drive to another, however was fine when moving files around within the same drive.
In the end I managed to make a new drawer on the system partition which I drag and dropped all the system directories into. I then rebooted using the AmigaOS 4.1 CD and ran the installer to install a clean Update 2 on the existing system partition. After this I managed to replace the offending Kicklayout file with one from the fresh install and then able to delete the newly installed Update 2 directories and move my original system back out of the temporary drawer  and everything was up and running as normal after reboot.
You are excused at this point if you have lost the will (I did for the best part of two weeks) or a little confused. In short it's best not to mess with Kicklayout, the tiny reduction in boot time just isn't worth the potential hassle. If you insist on giving this ago then check the list of mandatory modules on the AmigaOS Wiki carefully first, mkae sure you don't comment out any crucial drivers, and have a working backup disc handy!