Editing skaters outside of thugpro

How are custom skaters made outside of the Thug2/pro creator? for example: http://thpsx.com/creation-details/?obj=339
is a goat model, which as far as I know isn't possible with the Create a skater feature.

I would like to make something similar to the goat cas, but replacing the goat model with something else, How can this be done?

That was created using the PS2 version of THUG2 with a Gameshark code. The SKA file was then imported to the PC version of THUG2. If it works in this version, it will work in THUG Pro.