This happened with McDonald's before when they made their logo upside down that was supposed to celebrate women everywhere for International Women's Day back in 2018, but it was dubbed as a stunt. Even The Guardian called the McDonald's logo being upside down a stunt.
https://www.theguardian.com/business/2018/mar/08/mcdonalds-sign-international-womens-day
I doubt that M&Ms' limited time for flipping their logo upside down would work because this idea was proposed by McDonalds nearly 5 years ago and was dubbed as a stunt.