Last week's purchase of Rivet Software Inc. won't immediately change much about the Denver company. Equity Administration Solutions Inc., the Pleasanton, California-based company that bought Rivet, plans to keep Rivet's Denver office and its 70 employees. Madelaine Rohan, who had been CEO, stayed with the company to be vice president of the combined operation's international business. What's hoped for in the deal is expansion, said Michael Boese, Equity Administration CEO, and what motivated…