Is it possible to change my product descriptions before they are sent to Google Shopping?

This is not possible. Our system passes your product descriptions as-is to Google Shopping. The only changes made are to comply with their requirements. For example, the feed automatically strips HTML tags. It truncates the description (on a word boundary) if it is too long. It also substitutes the product title if the description is blank.

Google Shopping requires that the description submitted match the description displayed on your site. Therefore, in order to make changes, you must edit the product descriptions in your store. This is also better because your content has a single source, so you only need to edit it in one place.