Well, domino's are known to be fairly aggro as well, and all are in the damsel family.
But still, we're talking one small fish added, and they got lucky the clowns tolerate it.
We are giving general advice/opinions on here, so of course there will be rare exceptions to the rules, and I lean towards what is healthiest for the fish.
Keep in mind, the heavier the bioload on a tank, the more stress, and greater risk of disease or territory probs.
I'm sure that LFS has fairly easy access for equipment or WC's to counter that.