In fact, behind the scenes, the deed was already done.

Before Dr. Beck’s arrival, representatives from the E.P.A.’s major divisions had agreed on final wording for the rules that would be sent to the White House for approval. But they were told to wait until May 1, when Dr. Beck began her job as the acting assistant administrator for chemical safety.

Dr. Beck then spent her first weeks on the job pressing agency staff to rewrite the standards to reflect, in some cases, word for word, the chemical industry’s proposed changes, three staff members involved in the effort said. They asked not to be named for fear of losing their jobs.

Dr. Beck had unusual authority to make it happen.

When she was hired by the Trump administration, she was granted the status of “administratively determined” position. It is an unusual classification that means she was not hired based on a competitive process — as civil servants are — and she was also not identified as a political appointee. There are only about a dozen such posts at the E.P.A., among the 15,800 agency employees, and the jobs are typically reserved for technical experts, not managers with the authority to give orders.

Crucially, the special status meant that Dr. Beck did not have to abide by the ethics agreement Mr. Trump adopted in January, which bars political appointees in his administration from participating for two years “in any particular matter involving specific parties that is directly and substantially related to my former employer or former clients, including regulations and contracts.”

Her written offer of employment, obtained through a Freedom of Information Act request, also made it clear that Dr. Beck’s appointment was junior enough not to require Senate confirmation, which would have almost certainly delayed her arrival at the agency and prevented her from making changes to the rules ahead of the June deadline.

None of these arrangements raised concerns with the E.P.A.’s acting general counsel, Kevin S. Minoli, who issued a ruling on her unusual employment status. Mr. Minoli saw Dr. Beck’s background as a benefit, according to a memo he wrote that was reviewed by The Times.

“You have extensive prior experience with the regulated industry’s perspective and are already familiar with (and may well have authored) A.C.C. comments now under consideration,” he wrote, referring to the American Chemistry Council.