CBS has recast the role of Sean Reagan for its forthcoming drama “Boston Blue,” tapping Mika Amonsen to succeed Andrew Terraciano, who portrayed the character throughout the original show’s 14-season run. Amonsen joins series lead Donnie Wahlberg, who reprises his role as Det. Danny Reagan in the spinoff of the network’s long-running police procedural “Blue Bloods.” Set after Danny Reagan transfers from the NYPD to the Boston Police Department, the new series finds his son Sean already working as a Boston patrol officer, giving the father-son duo a chance to reconnect on the job. “Boston Blue” is overseen by showrunners Brandon Sonnier and Brandon Margolis and produced by CBS Studios in association with Jerry Bruckheimer Television and JBTV. The drama is scheduled to premiere this fall in the former “Blue Bloods” time slot, Fridays at 10 p.m. on CBS.