Usage:
-ability (remove) [ability id]

Gives the selected unit(s) the ability corresponding to the ability id. E.g. you could give a Footman the Bloodlust ability. If "remove" is added before the ability id, then it instead removes that ability.

To get ability ids, you can use -codeabilities to get a nice list of a unit's abilities. Some useful ability ids include "A0FV" (hero glow), "AInv" (hero inventory), "Amov" (movement), "Aatk" (attacking), etc.

Examples:
-ability A0FV
(Gives the unit(s) hero glow)

-ability remove Adef
(Removes Defend from the selected unit(s))