Bone Spurs. vs Superiror Tactics
Don't have the game with me, so, I'm going by memory:
- Superior Tactics requires you to commit a die; hence, you're not using the die to generate damage; hence Bone Spurs does not trigger
Hope this helps (otherwise please post the text on the cards)
This is what Bone Spur says:
Bone Spur "
For each (Strike) or (Cleave) result produced during this attack, the attacking unit suffers 1 damage. The target unit ignores all damage from this attack."
While committing the die does make it so that it's not used for damage, the Strike or Cleave result was still "produced" during the attack. Thus, I'd say, as written, that even using Superior Tactics would not stop the Citadel Guard from taking damage.
My answers to the OP's question:
1) Yes, retreats are not blocked, nor are the Strike results "committed" to Bone Spurs. So you could still use it to cause retreats.
2) Bone Spurs would still trigger, because although it's not used for it's normal effect, the result was still a Strike Result. Bone Spurs doesn't require that any damage was dealt from it. (For example, if a Weak unit rolled Cleave, it would still trigger Bone Spurs, even though Cleave would not have caused damage.