We don't have a way of grouping products that would allow you to apply changes or discounts to a selected group of products; in fact, we don't have a way of mass-editing products at all, though that's on the wishlist as a possible new feature once we roll out our new HTML-based Seller Admin to replace our current Flash-based Admin.
You might consider using Discounts to markdown your product prices for sale promotions, rather than editing each product's price directly; that way, you could set an Expiration Date for the discounts, so once the expiration passes, the price would return to normal, and you could delete or revive the discounts later at your leisure. It's also easier to create a series of similar discounts vs. editing a series of products. When you create a discount for one product and click Submit to save the discount, all the settings for that discount will remain visible, so you can just click the Products menu to select another product, then change the Discount Name and click Submit to save that discount, then repeat this for each additional product discount.
