Feed is on distance. Get too close and it'll go blade of woe. Cloak with magblade and it's only feed. But no, no toggle per say. It's purely on distance from the enemy.
PC Master Race
1001CP
8 Flawless Toons, all Classes.
Master Angler
Dro-M'artha Destroyer (at last)
Tamriel Hero
Grand Overlord
Every Skyshard
Down With BOP!