Any tips on how one can go in and alter an AC so that the airline name shows up with ATC?

here is the list of airline names FS9 ATC knows by default (you will need to use 'edit voice pack' (http://www.editvoicepack.com) if you want others):AB EXACESACTION AIRAEROFLOTAEROMEXICOAIR AFRIQUEAIR CANADAAIR CHINAAIR FORCEAIR FORCE ONEAIR FRANCEAIR INDIAAIR SHUTTLEAIR TAHITI NUIAIRWAVEALASKAALITALIAALL NIPPONALLEGHENYALLEGIANTALLEGROALOHAAMERICANAMERICAN PACIFICAMERIJETAMTRANANSETTANTILLEANANZAARGENTINAARMYARUBAASIANAAUSTRIANAVIANCAAVIATECABAHAMASAIRBANGLADESHIBIGBISCAYNEBIZ EXBLUE RIDGEBLUE STREAKBRITANNIACACTUSCAIRCANADIANCANDLERCANEXCARGOLUXCATHAYCHALLENGE AIR CARGOCHAUTAUQUACHINA SOUTHERNCITRUSCOAST GUARDCOMAIRCONDORCONTINENTALCORSAIRDELTADHLDOMINICANADRAGONAIRDREAM FLIGHTDYNASTYEAGLE FLIGHTEASTERNEGYPTAIREL ALELITEEMERALD HARBOR AIREMERYEUROPAEVAEVERGREENFED EXFINE AIRFINNAIRFIRST AIRFLAG SHIPFRENCH LINEFRONTIER FLIGHTGAIAGARUDAGEMINIGEORGIANGHANAGIANTGLOBAL FREIGHTWAYSGULF FLIGHTHAWAIIANHORIZONIBERIAICE AIRJAMAICAJAPAN AIRJET BLUEJET LINKJET SETJET USAJORDANIANKESTRELKITTY HAWKKLMKOREAN AIRKUWAITILAKES AIRLAN CHILELANDMARKLAPALAUDALEGENDARYLONG HORNLTULUFTHANSAMALAYSIANMALEVMARINEMARTINAIRMESABAMEXICANAMID EXMIDLANDMIDWAYMONARCHMOROC AIRNAVYNEW ZEALANDNIGERIANIGHT CARGONORTH AMERICANNORTHWESTOLYMPICOMNIONTARIOORANGEORBISORBITOZARKPACIFICAPAKISTANIPAN AMPHILIPPINEPOLAR TIGERPRO AIRQANTASRED ROCKREGIONALRYANSABENASAUDIASCANDINAVIANSHAMROCKSINGAPORESKY EXSKYTOURSKYWESTSOARSOBELAIRSPEED BIRDSPIRIT WINGSSPRINGBOKSUN COUNTRYSWISSAIRTACATAPTHAITRADEWINDSTRANSATTWAUNITEDUPSUS AIRUS AIR SHUTTLEVANGUARD AIRVARIGVASPVIRGINVOLGAVOYAGEWATER SKIWESTWEST INDIANWINDY CITYWISCONSINWORLDWORLD TRAVELYUKONZANTOPan airline name is not always the same as it's callsign. see this www for airline to callsign matches -http://www.geocities.com/hawaiian717/airinfo.html--

Add an airline name to the airlines.cfg file in the aircraft folder in FS2004.That will make the name selectable in the select aircraft list.You can copy the list above and paste it into the file if you wish.