Have you trued to assign a key combo in the keyboard controls file and see if it somehow switches on/off the TDC?
I also think this must be hardcoded, due to the different way the TDC operates from the german one. The US TDC was created to be autonomous from optics input expect in the exact moment when a bearing is sent from TBT/Scope. Therefore I also don't see any interest in being able to switch it on/off manually, just curious what would you gain with that?
