The Frelick move to some infield exposure didn't just happen this spring, it was started in the off-season with his work with Pedroia...and he does have some (minimal) history on the infield in his past. The interview with Adames (about Sal at third) wasn't super positive, but it wasn't negative either. As to his performance at the plate, having his hand healthy now will likely have more impact than his new defensive position.
I expect Sal to get the majority of time at third vs righties, and/or to move back and forth from there and the outfield in lots of games. Sanchez on the IL for a few weeks to start...and work on his rcvg...gives Bauers a brief reprieve, but if he doesn't produce he'll be on waivers when Sanchez is deemed ready.