This is another way to add Cardassian ships to the game if you have any of the Dominion Wars mods from Chris Jones. This works with the Beta Patch only (90% sure).MAKE BACK-UPS TO ALL FILES MENTIONED
Step 1-Make sure that all of the Cardassian,Dominion or Jem Hadar ship are under the "Cardassian" race in the Specs\DefaultLoadOut file.
Step 2-Then go to the CommonSettings\RaceNames.gf,you will see the race names of all the different races in the game. Switch the "Borg Collective" and "Cardassian Union" lines leaving the numbers the same(3="Cardassian Union" 5="Borg Collective"). Then do the same for the short race names at the bottom(3="Cardassian" 5="Borg")
Step 3-Then go to CommonSettings\ItemRules.gf. You will see a line that says MixRacialTech = 0. Change the 0 to a 3 to "turn off" the mixing racial tech. Then put a name of one of your Cardassians ships in the line 3="Sphere.Mine Says 3 ="Dominion Heavy Cruiser"
Step 4-Go to your items in the CommonSettings folder(BridgeItems,HullItems,PowerItems,ShieldItems,WeaponItems). You will see the Items and on the most bottom line(sometimes second to most bottom) there is a line that says Race="F,K,R or B or any combination" example Race = "F". What ever Items you want for the Cardassians,put a "B" in the quotation marks. More than one letter can be in it.
Step 5-Go to SFC3\MetaAssets\ServerProfiles\SinglePlayer\Character.gf. Go to the bottom ,go to every line 3="something" (there are 3 of them for every difficulty) and change them to one of your Cardassian ships(FF or DD would be best)
There you have it,the Cardassins are in SFC3. But you probably need to add the Cardassian bases and a shuttle to the DefaultCore and DefaultLoadout Files. Have any questions, send me a private message.