A bit of contribution for your consideration. You should consider adding a bit of code to the script to check what aircraft you are loading, otherwise your hardware fuelcutoff buttons may stop working for other aircraft you use. Also, the ixeg dataref you are commanding is only available when the IXEG bird is loaded and will lead to a lua error/stop when loading a different aircraft.
So the script provided you above, i would suggest as follows:
if PLANE_ICAO == "B733" then
-- Engine 1 cutoff switch
create_switch(15, "sim/flightmodel/engine/ENGN_mixt", 0, 1, 0)
create_switch(15, "ixeg/733/fuel/fuel_start_lever1_act", 0, 1, 0)
-- Engine 2 cutoff switch
create_switch(17, "sim/flightmodel/engine/ENGN_mixt", 1, 1, 0)
create_switch(17, "ixeg/733/fuel/fuel_start_lever2_act", 0, 1, 0)
end
note: by adding those simple lines, the buttons customization will only trigger when loading the IXEG 737, you may also add easily additional entries for different aircrafts if those use different datarefs for fuel cut off.
hope this helps