This link will tell you all you need to know:
http://db.gamefaqs.com/computer/dosw...ar_editing.txt

I didn't write this, but its what i used to learn how to change the basic functions of units. (Big thanx to the author)

Its a credit to the developers that such changes can be made and undone (back up the file!) with ease.

It doesn't make a massive difference to the gameplay, but i think its noticable.