One of the latest features to the batch update tool is a way to batch update the sell price or buy price percentage of a certain variant/condition. This batch update option is located on the "Variants" tab of the batch update section, 2nd from the bottom:
When using this batch update, you will need to have a product type selected, as well as at least one variant under the variant specific filters. When you perform a batch update using this option, it will disable the default price/buy price percentage of that variant on the included products, and use the percentage you specify instead.
For example, let's say we have Light Play set to 90% in the product type:
We can select a particular set category, the Light Play variant, and choose "Set sell_price % to 80%".
When we batch update, the Light Play conditions for just that set will be 80% instead of the default 90%.