Simplest method would be to edit the .mat file. On the other hand, there are r_specular and r_hardness console variables in the game, but they act as multipliers, not the default values. It would be possible to change them to be the deafult values, or, even better, introduce a new r_default_specular and r_default_hardness variables.
Edit:
I mean, the values in the .mat file just replace the default parameters, so creating them will result in the very same image as by changing the default values. They are treated just the same.