Starboard Value is continuing its activist campaign against Yahoo Inc with an open letter to Yahoo CEO Marissa Mayer that pushes for a Yahoo-AOL merger and issues a veiled threat that a “significant leadership change” could be necessary if Yahoo doesn’t comply. Starboard Value: Yahoo should consider a merger with AOL “We continue to believe that Yahoo must significantly reduce costs to improve profitability in its core business and should be considering a combination with AOL,” writes Starboard Value managing member Jeffrey Smith. “A combination with AOL, structured properly, could accomplish all of these goals by allowing for: (i) a…