oops - I'm thinking u mean add a custom flag...if so, this is from the tute here at OFPEC:
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First, I recommend creating a folder named "Flags" in your "OperationFlashpoint" folder. You can use it to store all of your flag images.
Flags must be in JPG (non-progressive) or PAC format, with a size of 256x128 or 128x128. You can convert JPGs to PACs by using the TexView program; it saves the file as a .PAA file, but you can rename it to .PAC. Caution, if saving as .PAC image, be sure not to use the same names as the official flagpack, ie usa_vlajka.pac, rus_vlajka.pac, white.pac, and quite a few more. I recommend putting your initials at the beginning of the filename with a dash or underscore between it and the rest of the name.
Once you have the images created and saved to the "Flags" folder we can start the editing...
Open two sessions of Windows Explorer; navigate 1st one to the "Flags" folder, and 2nd to the folder with the name of the mission you are editing (contains the mission.sqm file). Copy the flags that you want to use from the "Flags" folder to the "MissionName" folder.
Now, in the mission editor, add a flagpole where you want it and put the following in the initialization field:
this setflagtexture "flagfilename.jpg";
or
this setflagtexture "flagfilename.pac";
That's all there is to it, now when you save your mission as a multiplayer mission, it compresses the flags into the mission .pbo file. Everyone that plays the mission will be able to see the flags whether they have the flags already or not.