Just install as usual, the Power "Leave combat" should be added to your spell list,
White Shadow said:
"This little mod was made upon personal request. It's a spell, which allows you to forcibly leave the combat state. It is primarily intended to get rid of the "You cannot use this while in combat"-issue, when already half across the map away from enemies.

This can be heavily exploited, since it can stop any aggression against the player. Permanently hostile targets will reengage you, if you are still in aggro range, however normally neutral NPCs (including guards) will completely forget about you. Bounties will stay, however guards will usually have to first confront you again before entering combat (may vary).

Using this while engaged in battle or while close to the attacking NPC can potentially have unforeseen effects or consequences. Use at your own risk!"