The volunteer municipal body that oversees the preservation of New Canaan’s historic district—God’s Acre and the buildings around it—had a new officer appointed to its commission during an odd, tense meeting Thursday. The former secretary of the Historic District Commission, Terry Spring, who had served on the five-member group since 2005, wasn’t reappointed by town officials earlier in the week. Instead, the Board of Selectmen appointed alternate Carl Rothbart as a regular member. Spring’s ousting meant that a new secretary had to be elected. Yet she attended the commission’s Jan.