Hi Max,
In VDDT you can set TSD values by State Class for individual records in the Initial Conditions screen. This is described on page 62 of the VDDT user manual. If you want these values to be randomized you will need to do the randomization outside of VDDT and then create multiple records for each state class, each with different TSD values. At the moment we are no longer developing VDDT but the ability to randomize by state class could be an enhancement we consider in the future for Path / ST-Sim.
Regards,
Leonardo