Community Tip - Did you get an answer that solved your problem? Please mark it as an Accepted Solution so others with the same problem can find the answer easily. X
I guess keyboard shorcuts are allowed to only have a single character + modifier keys. That means you could define a shortcut like Ctrl+Shift+Alt+F, but not sure, didn't test that in Creo Parametric 4.0 yet. Kinda limited, but it's done the same way in other CAD apps, such as SolidEdge and SpaceClaim 2016 as far as I know.
For multiple-character shortcuts for functionality, see mapkeys. These can invoke a single command as with keyboard shortcuts, or go further and do multiple commands, or do UI within the commands, etc.