How do you remove, add, and modify unit perks?

[Galgus]

I've been trying to learn by looking through the New Horizons mod, but it is a bit confusing.

When an upgrade is chosen does the game add perks on top of the unit, or is it a new unit with entirely new perks?

Any advice would be appreciated. My main goal is to make unique units feel more unique, likely with some combat strength nerfs to compensate promotions.

Aside from removing perks to add them to base unique units, I have no idea how to modify passive abilities like that of the Drone Cage with XML.

Ideally I'd also like to know how to allow them to be activated without requiring the unit to remain stationary - so they could move and then activate it - but I am even more confused by that.

This is the Drone Cage code that has me particularly puzzled, mostly with how to modify passive abilities.

Spoiler :

<Row>
<Type>UNIT_PASSIVEABILITY_DRONE_CAGE_AOE_HEAL</Type>
<Description>TXT_KEY_UNIT_PASSIVEABILITY_DRONE_CAGE_AOE_HEAL</Description>
<Help>TXT_KEY_UNIT_PASSIVEABILITY_DRONE_CAGE_AOE_HEAL_POPUP</Help>
<IconIndex>8</IconIndex>
<IconAtlas>UNIT_ACTION_ATLAS_2</IconAtlas>
<Range>1</Range>
<AOEDamage>-5</AOEDamage>
<AffectFriendly>true</AffectFriendly>
</Row>