Unfortunately, updating the attributes for a particular product class only changes the default attributes that are applied to newly created products. In other words, making changes to a class's attributes will not affect already existing product nodes. Moreover, you cannot by default make changes to the pricing, weight or other information for multiple products at once, as these settings are stored separately for each product.

The Product Retrospect module, however, offers the following functions:

Update attributes & options
Select any class and apply its current settings retroactively to all existing products that share that class.

Update product information
Select one or more settings from any product node (e.g. price, weight, shipping) and copy them to all products of a particular class at once.