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They handled the sales-resistance by publicly soft-pedaling it... but politely insisting on it, and pushing through what is best for the team.
I believe that the feedback they are looking for now is not the players' preferences -- but the on-field results defensively. It says here that the experiment will run until the last 10 games, and if Lopez can play 3B, that's where he'll be. If it becomes clear that he can't play 3B, he won't.
Seeing that Lopez *has* played 3B, including in the majors, I predict this won't be an issue. :- )