The way Creo works now I doubt you can do this with mapkeys.
Maybe the best option here is a external script: Autohotkey or Autoit (they are similar).
These programs send a series of programmed keystrokes to Creo. They aren´t so robust as mapkeys but in some situations are the best options.
This is how I would do it with Autoit:
WinWaitActive ("Dimension Properties"); Waits for the window of Dimension Properties to be active
Send("{RIGHT}^{TAB 6}{END}"); Sends a sequence of Keystrokes
Send("("); sends text for preffix
Send("{TAB}{HOME}")
Send(")"); sends text for suffix
Send("{TAB 10}{Enter}"); Sends a sequence of Keystrokes