Ok I am going to attempt to make this seem as easy as possible:
First press R1 to bring up the quick menu.
Choose the menu u would like to change and press and HOLD that directional button.
This will bring up a small box that gives you the option of changing the action.
Change the TEXT MESSAGE.
A text box will appear for you to customize your message.
After you have done this, click done. Now you have a custom message or "Hot keys" as they are often called.
NOTE: %4 can take the place of someone's name. This will allow you to make messages like this:
Hail %4.
If you were conned onto me it would read:
Hail Sypher.
(if %4 is not the correct number will someone please correct me..i'm not playing right now)