search for datcrypter. You decrypt the magic type, edit it and re-encrypt it.
If you search more on magictype you'll find lots of info about what each column means and if you look in modern sources (albetros being a good example) you can look at the magictype table generated from the magictype.dat which has all the columns labled for you! Yay convenience! ahaha.
Note: I'm referring to new magictypes. Old ones were not encrypted and could be edited with a hex editor.