The basics of the 738,000 square-foot project, which involves closing the Commonwealth Hall exhibition space but revamping ballroom and event space at Fidelity’s neighboring Seaport Hotel, did not change despite the pandemic, a spokesman said. And Fidelity, which has about 1,500 employees based in the building (though many are currently working from home), still plans a large office there when work is done. The height and general shape of the building, which sits on a pier over Boston Harbor, will not change.