Unfortunately not (if you mean the flag on their uniforms). Although SOME units do allow you to change their textures, but sadly not all, and I do not have a list of those units you can do it with - you'd just have to experiment. Try this on your unit:
unitName
setObjectTexture [0,'#(argb,8,8,3)color(0,1,0,1)'][/url]
If it turns GREEN, it means its textures can be changed. Otherwise, you're out of luck.
Wolfrug out.