I assume Creo Parametric's "open system window" functionality is running the command defined by the environment variable "ComSpec" which is typically C:\windows\system32\cmd.exe. I haven't tested this. It's simply my assumption.
If my assumption is true, try changing the ComSpec variable in the .psf file [or at the System/User environment level].
There are alternatives to the cmd.exe file. A simple search should give multiple results.