I think this might be helpful:
<?xml version="1.0" standalone="no"?>
<upgrade>
<image path="images/merlin_touch.bmp"/>
<image-cancel path="../cauldren/images/dark_magic_upgrade_cancel.bmp"/>
<time value="300"/>
<unit-requirements/>
<upgrade-requirements/>
<resource-requirements>
<resource name="gold" amount="300"/>
</resource-requirements>
<effects>
<unit name="dark_mage"/>
<unit name="reaper"/>
<unit name="tartaro"/>
<unit name="wyvern"/>
<unit name="witch"/>
<unit name="shadow_walker"/>
</effects>
<max-hp value="300"/>
<max-ep value="0"/>
<sight value="0"/>
<attack-strenght value="0"/>
<attack-range value="0"/>
<armor value="0"/>
<move-speed value="0"/>
<production-speed value="0"/>
</upgrade>
It is the code for the Merlin Touch upgrade. You can add HP or EP reserve, but I doubt you can add regeneration.