I dont think you can, you prob could? You have to do it in ur fsx.cfg file. FSX is little different then FS9 , cause i remember removing the brake signs and all in FS9, but never tried in FSX.
see how it goes.. whatever the case is, it should be a "0" at the end of the statement to turn it off.. since it uses boolean terms of True and False.
You can edit the language.dll of fsx to exclude those messages by using a tool called 'resourcehacker. You'll find a description of the simple procedure at this link: http://www.sim-outhouse.com/sohforums/s ... post343583