[chirp_users] CHIRP VHF / UHF band "low / high" band limits ?

We are a state law enforcement office using CHIRP to program "QYT - KT 8900 D" units for use in our prisoner transport and patrol vehicles. Our area (Greater Pittsburgh, PA) is one of the few areas nationwide where due to congestion the "T-Band" UHF (480 - 520 Mhz) is in use. Under the "Settings - Other Setting" tabs on CHIRP the band limits are "grayed out", preset to 136 - 174 Mhz VHF and 400 - 480 Mhz UHF. How can we change the "high" (upper) band limit for UHF from 480 Mhz to 520 Mhz ?