The part to look at is EQType. 22 is Mitigation, 403 is Evasion. So you'll need to make another entry like the current one, and change <EQType>22</EQType> to <EQType>403</EQType>. Then make adjustments to the Location X and Y settings so they're not on top of each other. You might want to change the label for the current Mitigation one, and have a separate label for the Evasion one. And finally, somewhere (probably near the bottom) there's a section with <Pieces>. You'll want to add your Evasion one there, and rename the Mitigation one to your new label if you did that.
Edit: And, for future reference, this page
is super helpful.
Double edit: Also, when doing something breaks the UI back to Default, check the UIErrors log in the base directory for EQ.