using afcad to modify an aiRfielDs i see it puts the modification in the C:Program FilesMicrosoft GamesFlight Simulator 9Addon Scenerysceneryfolder as af2_ICAO.bgl I SEE that the bases modified by ultimate traffic and my traffic also reside there. if i want my modification to be used do i need to remove the F1UT_ICAO.bgl and the MY_ICAO.bgl where the ICAO is the same?

Yes. Duplicate AFCADs can be a nice way to crash the sim.Rather than remove the files I change the file extension to .dupl. That way if I don't like the new AFCAD I can delete it and rename the old file back to .bgl. For example AF2_KLAX.bgl becomes AF2_KLAX.bgl.dupl.