Might downloading a 50-cent coupon for Cheerios cost you legal rights? General Mills, the maker of cereals like Cheerios and Chex as well as brands like Bisquick and Betty Crocker, has quietly added language to its website to alert consumers that they give up their right to sue the company if they download coupons, “join” it in online communities like Facebook, enter a company-sponsored sweepstakes or contest or interact with it in a variety of other ways. Instead, anyone who has received anything that could be construed as a benefit and who then has a dispute with the company over its products will have to use informal negotiation via email or go through arbitration to seek relief, according to the new terms posted on its site. In language added on Tuesday after The New York Times contacted it about the changes, General Mills seemed to go even further, suggesting that buying its products would bind consumers to those terms.