Once you have nocked an arrow and drawn in back it has always been impossible to put the arrow away without shooting it (without going into the inventory.) This mod will de-nock your equipped arrow when you press "spacebar." This works with both arrows and bolts. This mod is dependent upon Morrowind Script Extender (MWSE) v0.9.2a or later, or MGE v3 or later. There is a setup ring in the inventory that allows you to select what key to denock your arrow.
This mod is great, except that it doesn't prevent the durability hit to the weapon.