Adding More Groups in Per Item

[Ptool]

I downloaded the mod for the Group Pricing (Per Item), I have not had any problems so far, but I wanted to add a 5th group. I went into the files

Admin>Includes>Extra Data>Group_Price_Per_Item.php
Includes>Extra Data>Group_Price_Per_Item.php

I added the line:
define('GROUP_PRICE_PER_ITEM5', 'Group E');

Stating that it is 5th group and the name is Group E
Is there a file I am missing? Do i need to add this somewhere else?

Any help would be greatly appreciated =)