It's not quite so straightforward - what a surprise.
Some notes from PANS OPS and the Airbus manuals
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Vat - Speed at threshold based on 1.3 times stall speed Vso or 1.23 times stall speed Vs1g in the landing configuration at maximum certificated landing mass.
The landing configuration which is to be taken into consideration shall be defined by the operator or by the aeroplane manufacturer.
Because aircraft of the A320 family have a low-speed protection feature (alpha limit) that the flight crew cannot override, the airworthiness authorities have reconsidered the definition of stall speed for these aircraft.
All the operating speeds must be referenced to a speed that can be demonstrated by flight test. This speed is designated VS1g.
Airworthiness authorities have agreed that a factor of 0.94 represents the relationship between VS1g for aircraft of the A320 family and VSmin for conventional aircraft types. As a result the authorities allow aircraft of the A320 family to use the following factors :
V2 = 1.2 × 0.94 VS1g = 1.13 VS1g
VREF = 1.3 × 0.94 VS1g = 1.23 VS1g
These speeds are identical to those that the conventional 94 % rule would have defined for these aircraft. The A319, A320 and A321 have exactly the same maneuver margin that a conventional aircraft would have at its reference speeds.
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So the PIC really cannot (should not??) just change it a it is a declared figure.
Hope that is of some help