First, could President Trump “open up our libel laws”? No. States create nearly all libel laws, and they’re subject to First Amendment limits. Trump couldn’t require states to change their laws, any more than he could require the Supreme Court to change its First Amendment jurisprudence, or require Congress to rewrite the First Amendment. This is a matter of eighth-grade civics.
Second, could President Trump change the Freedom of Information Act? Kind of. He alone couldn’t amend the law, but he could affect its implementation. For example, on his first full day in office, President Barack Obama signed one executive order and two presidential memoranda heralding a “new era of openness” that would, among other things, re-establish a presumption of disclosure for records requested under the FOIA—and reverse President George W. Bush’s changes to the Presidential Records Act, to hold his own records “to a new standard of openness.”
Third, could President Trump crack down on public affairs reporting? Yes, most likely in the area of national security—if his Department of Justice prosecuted journalists under, say, the Espionage Act, something that has occurred once before, or if his DOJ tried to obtain an injunction against publication, or prosecuted leakers and subpoenaed journalists to supply information. Another route would be to issue an executive order modifying how classified information must be handled, or allowing information to be classified for longer periods.
Fourth, what if President Trump simply didn’t like the press, as he’s been saying on the campaign trail? What impact could that have? It could mean Trump would be less accessible to journalists or wouldn’t invite them to certain functions or press conferences.