This is something i had plenty of problems trying to find. Most people would suspect this is hidden in GRUB but this is not the case. Its hidden in the initscripts.

HowTo: Remove or Customize "Welcome To Fedora" boot message. (Ref init-message).

 Easy way. (Not the right way!) to do this.  (Read More)

Open /etc/rc.d/rc.sysinit in your favorate text editor. 

Search for this section:

Print a text banner.

 Look for this section.

 elif [[ "$redhat_release" =~ "Fedora" ]]; then
 [ "$BOOTUP" = "color" ] && echo -en "\\033[0;34m"
 echo -en "Fedora"
 [ "$BOOTUP" = "color" ] && echo -en "\\033[0;39m"

Change the BOLD text to whatever you want displayed. 

Save the file and reboot.

 You now can show a custom message on boot (Right before loading Interactive setup.)

 If you want to do it the right way you should fix the file /etc/redhat-release or even rebuild the init package entirely while patching needed locations. The way i explain is to help you get going, its a quick fun trick you can do to customize your system a little more. Or its a good pointer on the right path to building a Fedora based distributioin (Rebranding requirements). 

Hope this helps!