You just change the file directory to make it read FPS Creator on the folder instead of demo/trial. Change the setup level under languagebank/english/gamebank/mygame; and look around and change all other texts that say "FPSC Trial" or something to that effect. If you want, download one of the updates 1.02-4 and save them to the directory you created. Now just copy the custom media into the correct folders.
P.S. I did do this successfully, but it was a very long time ago so
I can't assure you it will work.
"Its not how many times you fall its how many times you get back up!"