You don't edit the armor values. You edit only the frontal/rear penetration, accuracy and received damage values against a given weapon. You would need to find the weapon you want to edit and tweak the stats of it vs Jagdpanther armor.
In example, SU-85 weapon is strong against Jagdpanther, so you go to the SU-85 weapon, to the target table and edit the weapon stats you want to make it weaker. That's it.