
Copy or clone all the lines of the original unit and rename it accordingly. After this select "building_units_allowed". In order to do this, select and expand the "building_levels_tables" under the "db" directory.
The first file we are going to edit is "building_units_allowed". Choose the unit you want to clone (use as a template), f.e. Open my_pack.pack with the Pack File Manager (It is in the /data folder of within installation directory). Creating a new unit (Based on The Phenom's excellent guides) To remove the mod simple delete the script and pack file. Those who have other mods already installed and understand the use of user.empire_script.txt will know they can edit their own script and rename the mod pack to what is suitable for them.
(I attached the zip file to this thread, because there were some problems with the attachment in the other thread.) Unpack the zip and put user.empire_script.txt in your C:\Documents and Settings\username\Application Data\The Creative Assembly\Empire\scripts (XP) and place the my_pack.pack in your C:\Program Files\Steam\SteamApps\common\empire total war\data folder (XP).
Download the Sample Mod Pack from here. Download the Pack File Manager (PFM) from here. If you have problems or suggestions, ideas, post them. There are still some unknown issue regarding unit creation (like changing an unit's 3D model), but you should be able to make your own custom unit if you follow this guide. This step-by-step guide was written by various members (see credits in the end) in various threads, I just tried to gather all the important information in one tutorial and added my thoughts as well. How to create a custom unit - a complete guide