quote Matt Jones @ SI Forums.

Here is a guide to using EDT and DDT files within FM 2005.

It is what SI has told me and is, therefore, official. If you have any questions regarding these files afterwards, I will do my best to help. With thanks to Keith Flannery for his reply.

1. EDT files
   The two EDT commands that have been tested and are supported for CM 03/04 are:
   
   “SWAP_TEAMS” and “BOOST_TEAM”
   
   The following is an example of what the contents of an EDT file look like:
   
   "SWAP_TEAMS" "Wolves" "Celtic"
   "SWAP_TEAMS" "Bolton" "Rangers"
   "BOOST_TEAM" "Celtic" 12000000 5000 22000
   "BOOST_TEAM" "Rangers" 15000000 6000 35000
   
   "SWAP_TEAMS" "Wolves" "Celtic" - used to put Celtic in the Premiership and Wolves into the Scottish Premier League.
   
   "BOOST_TEAM" "Watford" 20000000 7000 40000 = will set Watford's transfer budget to £20,000,000, change their reputation to 7,000 (max = 10,000), increase attendance at games to around 40,000 (If stadium capacity permits).
   
   Possible Issues:
   
   
   The "BOOST_TEAM" command does not adjust the teams wage budget at the moment.
   
   This feature has only been tested on certain leagues, so it's a case of try it and see.
   
   If you are bringing a team from an unselected league into a selected league then some of the lesser players will probably be missing from their squad.
   
   
   
2. DDT files
   The two DDT commands that have been tested and are supported for CM 03/04 are:
   
   “RETAIN_PLAYERS” and “RETAIN_NATION_PLAYERS”
   
   The following is an example of what the contents of a DDT file look like:
   
   "RETAIN_PLAYERS" "Celtic"
   "RETAIN_PLAYERS" "Rangers"
   "RETAIN_NATION_PLAYERS" "China PR"
   
   "RETAIN_PLAYERS" "Celtic" = will retain all of Celtics’ players upon starting a new game – if you put the old firm into the Premiership, you must make a file like this to ensure that they have full squads.
   
   "RETAIN_NATION_PLAYERS" "China PR" = will retain all players with a nationality of China PR.
   
   
3. Other Commands
   The other EDT and DDT commands are redundant in terms of use for the game and therefore haven’t been tested for either CM4 or CM 03-04. However, SI has made a decision not to disable their use in the game, but their use is at the users’ discretion.
   
   
4. How do I make them and where do they go?
   EDT and DDT files are created in notepad. When you go into notepad, and have finished typing in your commands, click File. Then, click Save. In the dialog box that appears, select “All Files” for the file type (this option is near the bottom). Then, type in whateveryouwant.edt or whateveryouwant.ddt (obviously changing “whateveryouwant” to something more memorable).
   
   Save them in the “C: \Program Files\Eidos\CM 03-04\data\db” directory (where “C: \” is the letter of your hard drive).
   The only thing that the check boxes on the preferences screen do is to rename the file within the directory mentioned above from *.edt to *.edd and from *.ddt to *.ddd to effectively disable them from being read by the game upon starting a new game.