Could one use this method to update from 3.15 to 3.16 without having to use a CD or USB?

like this for my macmini:
1. Extract the iso file into a folder somewhere.
2. Use Mounter to mount the Boot partion.
3. Copy mac_ppc32/boot.img into Boot:
4. Bless the boot.img file using 'HFSSetMacBoot Boot:boot.img' (*1)
5. Reboot
6. Run the update setup from the extracted iso folder


*1 : This part I find a bit confusing.
Reading the boot.txt it says you need to bless the boot.img file.
Further down it also says its important to bless the bootinfo.txt file if it have been edited.
But the information also say "It is only possible to bless one file per partition."
Now, in my case I should only need to bless the boot.img file, since I have not touched the bootinfo.txt file.