Advanced Pricing Rules
Advanced Pricing Rules apply to Marketplace Plugins.
You can choose to have a flat percentage to increase or decrease pricing. (To set a decrease, just enter in a minus sign on the number. If you select "with more advanced pricing options below", click Update. You can then build a set of pricing rules to take products up or down based on categories or manufacturers or price ranges.
Keep in mind that pricing rules get executed in order. If you enter in a rule for all products to go down 10%, and then set another rule for a specific manufacturer to go up 4 dollars, that rule will supercede the rule above it for that peticular manufacturer, and that manufacturers products would only go up by 4 dollars.
You can use this method as a way to set an exception on a category or manufacturer (eg: increase the price by .00001% would effectively not change the price for that category or manufacturer. Once a rule is set, it can be deleted or modified.