The positional change involving two established players can go rather seamlessly. Example:

As a condition of his trade from the Rangers to the Yankees, Alex Rodriguez agreed to move to third base with the established captain, Derek Jeter, at short — though most unbiased onlookers would have ranked A-Rod as the superior defender. Well, at least at the outset it was without the tension over who would play where.

Or it can fail to go seamlessly. Example:

The Mets obtained Mike Piazza in mid-May 1998 while the starting catcher, Todd Hundley, was recovering from elbow surgery. Infuriated that he lost his job while injured, Hundley uncomfortably moved to left field upon his mid-July return, was so bad that the experiment was halted five weeks later and Hundley was traded after the season.