First-year manager Bo Porter held his first closed-door clubhouse meeting Tuesday at Osceola County Stadium. Porter’s message to the rebuilding Astros: Everything is new. Let’s go compete. Astros pitchers and catchers held their first official spring-training workout Tuesday after reporting Monday. About 15 position players joined the group, and Astros’ athletes, coaches and front-office members converged in the team’s clubhouse before taking the field. “We talked about the change and you can look around and tell that things are changing. … Embrace the change and embrace the opportunity, and we’re looking for guys to take the bull by the horn and run with the opportunity,” Porter said. Highlights from Porter’s pre-workout media session: The Astros manager said the club will embrace Roger Clemens with open arms when he appears in Kissimmee to serve as a spring-training instructor. Clemens is scheduled to appear three separate times, with his first appearance tentatively set for Sunday. Porter said Bud Norris and Lucas Harrell are the only locks for the team’s starting rotation. Jordan Lyles, who’s long been mentioned as the Astros’ No. 3 starter, will have to compete for a spot. Porter emphasized Lyles will likely be a 1-5 starter, but he wants the Astros’ spring training to be as competitive as possible. “We want to make sure that we’re filling our roster with the best 25 guys that we can fill our roster with as we leave spring training,” Porter said.