Paramount reps confirmed Monday that the studio’s “Lassie” project is switching helmers, with Daniel Petrie Sr. replacing Dick Pierce.Petrie, who directed “Rocket Gibraltar,””Fort Apache, the Bronx” and “Cocoon: The Return,” was brought on board late last week after Pierce’s interest in the pooch pic waned, according to sources. Pierce’s United Talent Agency rep David Kanter had no comment. Sources said Pierce’s bone of contention was Paramount’s reportedly over-eager production sked, which would rush the dog movie into fall production. A fall shoot would have created problems for the pic’s “summery” look, sources added. “Lassie” is a big-screen adaptation of the popular TV series starring the clever collie of the same name.