I don't want all the available missions spys now have available to be in use. What file/tag turns OFF certain missions like Destroy building or Steal Plans?

Thanks.

I don't know if this is the only place where this could be done, but certainly you could remove sections of BTS\Assets\XML\GameInfo\CIV4EspionageMissionInfo.x ml to do this. Create a backup copy first, of course.

Concerning that file, Civ4EspionageMissionInfos.xml, if I give a mission an, <iCost>-1</iCost>, will that eliminate it from use?

Sorry, no idea. You could try it, or poke around in the SDK code for espionage mission infos to find out.

I did try it, and it appears to work. If you put the espionagemission cost as -1, it is eliminated from the menu of choices for spy missions.