Ownership of The Daily Telegraph, the storied British newspaper long considered close to the country’s Conservative Party, is poised to change — again. RedBird Capital Partners, an American investment firm, said on Friday that it had reached an agreement in principle to buy control of the newspaper’s parent company, Telegraph Media Group, at a valuation of 500 million pounds, or about $675 million. Friday’s deal is the latest twist in a long-running takeover drama for The Telegraph, which for much of its 170-year history has been considered a house organ of sorts for Britain’s Conservative Party. RedBird had already bought control of the newspaper via a joint venture with International Media Investments, a fund controlled by a member of Abu Dhabi’s royal family. Under that plan, the newspaper would have been overseen by Jeff Zucker, the former president of CNN.