Cards are not replaced during the "as played" window. The cancelation must be played immediately: no other effects can be used, except for wakes (eg. neither The Barrens nor Dreams of the Sphinx can be used).
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Tranquility
Only usable by a ready vampire not involved in combat.
Cancel a frenzy card as it is played (no cost is paid).
As above, and the target of the frenzy card gets an optional press, only usable to end combat.
Rulings
If the canceled card had a "do not replace until" clause (or alternate replacement like Steely Tenacity), that clause is canceled as well and the card is replaced normally.
The canceled card has still been played. The same reaction or modifier cannot be played again by the same minion. Any card which text prohibits to play more than once cannot be played again.
If a limited effect is canceled (bleed, additional strike), then the limit is not triggered and another limited effect can be used.
A card played "as if from hand" can be canceled "as played"
The optional press can only be used during the current round.