Can this serious of actions be considered legal?

1) Before I declare Hama as an attacker I play Unseen Strike on him.

2) Declare Hama as an attacker.

3) Trade Unseen Strike back into my hand.

4) Play Unseen Strike on Hama again.

I ask this, because I'm playing the Journey quest with the starting Troll. My Threat was at 26, so I pulled the troll and feinted him. Then using the actions above with another hero's help, I killed the troll. Hama would have 9 attack strength at that point.

I see nothing wrong with that. You can take actions before declaring an attack and US lasts the whole phase.

On a side note, cardgamedb has a hilarious typo for US in the textual form, "…while attaching an enemy…"