I wanted to find out if you could "fire" a steward by recruiting them into the Blades. So I took Iona, who is steward at Winstad Manor and made a Blade out of her. Despite Delphine telling me new Blades would have to stay at Skyhaven Temple, however, the next few times I visted Winstad Manor, Iona was there, only now she was wearing her Blade's armor.

Once a steward, always a steward, I guess. At least until they die.