I don't know that it is possible for one side to take over for the other, but the direction of loading on your shoulders is going to be ever so slightly different. Maybe a degree or so. Hence why I alternate hands while deadlifting.
I don't use mixed grip on shrugs because I use really heavy weights and lift it explosively. Doing that I'd rather not have either hand under the bar for fear of biceps. I wouldn't be as concerned with it creating an imbalance your shoulder growth.