Sectarus can be used to place a "Rise Again" on a creature. However, to place the enchantment the sword must damage it's target. Therefore, damage must be applied, and if that damage would kill the target then there is no one to cast "Rise Again" on.
The Power Rune only works with items that give you spell actions. Discount ring while awesome, are not improved by the Power Rune. The Horn of Gothos does not give you a spell action. It has a triggered ability that occurs when you use your battle orders. So, it is not improved by the Power Rune either. Even with that said the Power Rune can be used in conjunction with Elemental Wand, Mage Wand, Helm of Command, Wand of Healing, and Dispel Wand.
The disable ability is pretty simple. If it is a trait, then it stays, but if it grants another object a trait then it's gone. Basically, traits are a pretty intrinsic part of an object, but things like Dragonscale Hauberk that grant the Armor +2 trait to a mage, can be turned off because that is the ability of the equipment, to grant that trait to another object.