You could look at the animation's timelines, Animation timelines, find the AttachmentTimeline, remove it from the animation until you want it to be applied. This will affect all skeleton instances, who share the animation instances.
However, it might be easier to play different animation. Eg, if you are at idle, instead of playing attack, play idleToAttack which doesn't key the attachment changes during your mix duration. Or, if you want a single attack animation, play an animation that is the brief transition to the attack, then play attack.
