By changing the aggregation weight attribute on the Node Attributes tab, you can modify the relationship between the selected Custom member and its parent. See Defining Custom Members.
The aggregation weight for the Custom dimension can be any value (positive or negative), and fractions are allowed (for example, 1.5 is valid). The default values are 0 (no aggregation) and 1 (to aggregate). If the value is not 0 or 1, then the child member is aggregated to the parent using that multiplier.