Welcome to TWC, LordDRAKKON!

If you're new to modding the first thing you'll need is a modding tool, suck as Pack File Manager. This allows you to open the game's .pack files, to create mod files, to import databases from them into your mod files, and to edit the databases you have imported.

The second thing you'll need is modding guides, you'll find them in the Empire Mod Workshop. You might also want to use Pack File Manager to look inside mods which change flags, to see if this shows you how this is done. (Unfortunately, I can't tell you how to edit flags. Some modders have done this, so obviously it's possible).

Good luck!