If another effect also sets the range, the first to resolve has priority.
101878
Storm Sewers
Master: unique location.
You may lock this card as a minion you control announces an action. If the action is blocked, the range of each round of the resulting combat is automatically close. Skip the determine range step each round.
Rulings
Once the range is set, no other effect can be used to reset the range that round, but other pre-range effects can be played afterwards. Skip the Determine Range step for that round.
If another effect was already setting that round's range (e.g. Neutral Guard), that effect has priority.