To change the price of a child product within a promotion, you can use the following methods:

Adjustment (B): This refers to applying a price adjustment to the product, either by a fixed amount or a percentage, which modifies the original price based on the terms of the promotion.

Override (C): This method involves setting a new price that overrides the original price of the product within the context of the promotion.

Both methods allow for flexible pricing strategies within promotions, enabling customized pricing options that can be tailored to specific marketing objectives or customer segments.