The Spaghetti Warehouse, that aging paragon of pleasantly prepared pasta, is undergoing a few key changes that will make the restaurant fit for another several decades, a company official said. Even so, the improvements are going to be subtle and relatively drawn out, said Jeremy McLean, operating partner of BLD Brands, a California-based investment group that owns the Franklinton Spaghetti Warehouse. There are four other Spaghetti Warehouses — in Dayton, Toledo, Akron and Syracuse, New York — not affiliated with BLD. The Columbus restaurant is 43 years old, situated a historic 20,000-square-foot building at 397 W. Broad St. (the front door actually faces West State Street).