CustomisablePriority would be used to define whether or not a priority for a part (or function) can be customised. An example of where this would be used is for crew quarters that use crew location as a hack to have crew idle in specific locations and not move. While another system could be used for this, CustomisablePriority may have usage elsewhere in other parts. Simply put, if set to false, the specific priority will always use DefaultPriority and not be allowed to be customised.
USAGE
AmmoStorageA
{
Type = AmmoConsumer
AmmoType = bullet
MaxAmmo = 6
CustomisablePriority = False
DefaultPriority = &/PRIORITIES/Defense_Supply
AmmoDesireToggle = PowerToggle
ReceiveAmmoMediaEffects = &/COMMON_EFFECTS/PowerDeliver
}