Here's a trick I stumbled across by accident.  I'll use my 747 as an example of editing the aircraft.cfg file.

If you just want ATC to call you something else change

(flightsim.0) ...
atc_airline=Global (or whatever it is right now), to
atc_airline=Lufthansa (or whatever you want ATC to call it)

If you want to dump the default textures, and I have only tried this with replacements to default textures, download a Lufthansa 747 which is designed as a replacement and put it in the 747_400\texture folder.  Make sure that:

title=Boeing 747-400

Just to be safe I would back up the \texture folder AND the aircraft.cfg file.

If you want to add another one (mine is Swissair) do the same thing for /texture.1 and further edit aircraft.cfg to read:

(flightsim.1) ...
title=Boeing 747-400 Paint1 ...
atc_airline=Swissair

It is very important that the "title" section not be disturbed - it must say Paint 1, Paint 2, etc. - because that's where FS looks for the AI information. And you have to make sure that atc_airline is one of the supported ATC airlines.  There is a list here
http://www.fsgateway.com/tips_read.asp?id=411

That's how to turn the default aircraft into AI aircraft with real liveries.  There is another program to create other AI's and flight plans but I don't use it.  I'm sure someone will come along and tell you about it.

Sounds like what you is want is Lee Swordy's 'Traffic Tools', a utility to modify the traffic.bgl file that controls AI flights, found here http://www.simviation.com/fs2002utilities_ess1.htm

You might also want to grab the 'Aircraft Export Tool' from the same page. Though I havent used it, it may save considerable typing if you have many a/c you want to make AI.  Be advised that not all add-on a/c work well as AI, though repaints of default a/c should work fine.

Cheers,
Dave

Be careful, when editing the traffic, one minor mistake can really throw stuff off. And remember, AI wont fly in or out of airports with no tower (yes is bs i know, but thats how it works)