We announced to have stopped developement for FSX in 2017 so, we now consider it to run in "Life support" mode.
After we added the custom logo method in P3D V4 which works so much better than before, and is so much efficient and easier for users, we retired the old PaintKit, which suggested a rather complex method to add custom operators in FSX, which also had consequences, like adding too many objects variations for each new operator added, which slowed down the sim startup and took precious RAM you don't have in FSX.
So, we don't officially support methods to add custom operators in FSX anymore. You CAN add them, in theory, but it's very cumbersome, it would be easier if you would just make a list of the operators you are missing, in which airport, and we might just add them with an update.