Can a Kensei monk spend a bonus action to use the Kensei's Shot feature after they make an attack roll, and still do the extra damage on that attack?

Question

The Way of the Kensei monk's Path of the Kensei feature grants several benefits, including Kensei's Shot. The wording of Kensei's Shot is as follows (Xanathar's Guide to Everything, p. 34):

You can use a bonus action on your turn to make your ranged attacks with a kensei weapon more deadly. When you do so, any target you hit with a ranged attack using a kensei weapon takes an extra 1d4 damage of the weapon’s type. You retain this benefit until the end of the current turn.

Can you choose to spend the bonus action to use Kensei's Shot after rolling to hit, and still gain the extra damage on the attack you just made? Or do you have to declare that you're using Kensei's Shot before you make the attack roll?

Answer 1

Before you attack

You cannot take a bonus action while an attack is resolving. The structure of attack is:

1. Choose a target. Pick a target within your attack's range: a creature, an object, or a location.
2. Determine modifiers. The DM determines whether the target has cover and whether you have advantage or disadvantage against the target. In addition, spells, special abilities, and other effects can apply penalties or bonuses to your attack roll.
3. Resolve the attack. You make the attack roll. On a hit, you roll damage, unless the particular attack has rules that specify otherwise. Some attacks cause special effects in addition to or instead of damage.

Basic Rules: Making an Attack

Rolling the damage is an integral part of one attack. You cannot wait until the attack is declared hit/miss before committing your bonus action to improve the damage. You must do so before the attack.

You, however, can use Kensei's Shot after the attack resolves. If you have Extra Attack, you can then utilize the bonus damage on your subsequent attacks.