Well that’s how nothing ever changes. Personally, I will hassle the clerk until he seriously considers working somewhere else. That’s how we get change!
So, if you want to work for change, the first thing you need to do is to stop spending money in those stores. Every dollar spent at a business is a vote encouraging them to keep doing whatever they're doing.
The second thing to do is to let corporate know you're not shopping there and why.
Those things won't have a huge effect unless lots of people do them, but they'll have a much greater effect than harassing the poor front-line workers.