I have a question about using Blessing of Valaya and how it may affect how damage must be assigned during combat.

If you use Bessing of Valaya on a defending unit before damage is assigned, will the damage assigned by the attacker have to include an additional 2 Damage before damage can be assigned to the capital.

The FAQ states that enough damage must be assigned to destroy defending units before any damage can be dealt to the capital, if the attacker knows before assigning damage that 2 damage will be redirected due to the BofV, then I believe you would have to assign 2 more and only then can you assign damage to the capital.

If the card may be played after defenders are declared and before damage is assigned and the effect remains, then I'd say yes.

Check the FAQ/Rules to see how tactic cards resolve to be sure.