From the flight model file, these are the last lines of the weight and balance section:
max_number_of_stations = 6 ; Number of payload stations
station_load.0 = 170, 6.2, -1.5, 1.6, TT:MENU.PAYLOAD.PILOT, 1
station_load.1 = 170, 6.2, 1.5, 1.6, TT:MENU.PAYLOAD.COPILOT, 2
station_load.2 = 170, 0, -1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
station_load.3 = 170, 0, 1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
station_load.4 = 170, -5.3, -1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
station_load.5 = 170, -5.3, 1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
Make the following changes in bold to enable the last four seats:
max_number_of_stations = 10 ; Number of payload stations
station_load.0 = 170, 6.2, -1.5, 1.6, TT:MENU.PAYLOAD.PILOT, 1
station_load.1 = 170, 6.2, 1.5, 1.6, TT:MENU.PAYLOAD.COPILOT, 2
station_load.2 = 170, 0, -1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
station_load.3 = 170, 0, 1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
station_load.4 = 170, -5.3, -1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
station_load.5 = 170, -5.3, 1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
station_load.6 = 170, -8.3, -1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
station_load.7 = 170, -8.3, 1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
station_load.8 = 170, -13.6, -1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
station_load.9 = 170, -13.6, 1.5, 1.6, TT:MENU.PAYLOAD.PASSENGER, 3
The longitudinal positions are an estimate, based on an estimated three feet between the centers of the second and third rows, then another 5.3’ to the fourth, just as there is a 5.3’ difference between the first and second.
This requires a manual edit of the file, so as always, make a backup copy before editing anything.