Step by step:
First check where you have the com.apple.Boot.plist file in the order the system will look for it. EFI partition (if you have one) or /Extra folder would be the first place to start. For example, fire up the Terminal and type:
to check the Extra folder. If com.apple.Boot.plist is in the list of files then edit this one (or follow the same procedure with your EFI partition if you have one), if not then look in the SystemConfiguration folder:
And the com.apple.Boot.plist file should be there. I like to make a copy to the desktop when editing system files just incase anything happens:
cp /Extra/com.apple.Boot.plist ~/Desktop
If the file was in /Extra or:
cp /Library/Preferences/SystemConfiguration/com.apple.Boot.plist ~/Desktop
If the file was in SystemConfiguration. Now the plist will be on the desktop:
Cmnd D (it will read Alt D because of the windows keyboard layout if you didnt switch the keys around on the mini)
Will duplicate the file incase anything happens. This is a really simple edit and nothing should go wrong but I think its a good habit in general.
Then edit the original .plist file. The part that reads:
Needs to be changed to:
Save and close the file.
Now put the file back to where you found it:
sudo mv ~/Desktop/com.apple.boot.plist /Extra
sudo mv ~/Desktop/com.apple.boot.plist /Library/Preferences/SystemConfiguration
Restart, and if the computer doesnt blow up you can erase the duplicate .plist from the desktop.
Hopefully doing simple stuff like this will help you feel your way around the system and the terminal. The commands should be pretty obvious:
ls for list, cp for copy, mv for move etc. Each command also has a bunch of extra syntax you can add to be more specific if you need (like ls -a will list you all the hidden files as well, ls -A will list you the hidden files except for the working directory and parent directory, etc). Then sudo for superuser do, allowing you to do whatever you want, edit system files, etc. If the terminal returns "Permission denied" when you try to do something, youll need to run as superuser. Obviously take this as a warning to be slightly more careful if you dont know what youre doing.
Hope this helped.