Can an opponent play Siphon Power after damage has been assigned during the showdown damage step, and would that require re-arranging the damage spread?

Ruling: Once players pass priority in succession during showdown and reach the damage calculation step, no more spells or effects can be played. The opponent must activate Siphon Power before the damage calculation step is reached.

Sequence:

• During showdown, players have priority to play spells/effects
• Once all players pass priority in succession, damage is divided
• After damage division begins, no more spells or effects can be played
• Any spell like Siphon Power must be activated after the attacker passes priority but before reaching the damage calculation step