ItemPropertyDecreaseAbility

From NWN2Wiki

// Return Item property decrease ability score.  You must specify the ability
// constant(IP_CONST_ABILITY_*) and the modifier constant.  The modifier must be
// a POSITIVE integer between 1 and 10 (ie. 1 = -1).
itemproperty ItemPropertyDecreaseAbility(int nAbility, int nModifier);

Note: The values for IP_CONST_ABILITY_* are consistent with ABILITY_* and thus are interchangable