The main concession that House Republican leaders have made in their health-care bill to their most conservative members is far less sweeping than it appears and could create chaotic rules for the nation’s health insurers.

The change to the American Health Care Act, as the legislation is called, would compel each state to decide on the kinds of medical services that health plans must include. It was made in response to demands by the House Freedom Caucus, a group of rebellious, conservative lawmakers eager to weaken the federal role in health care and lower the price of insurance — in part by allowing Americans to buy skimpier coverage.

The caucus has been pushing to erase federal rules, created under the Affordable Care Act, that require plans to cover a set of 10 “essential health benefits.”

But a wrinkle in the House amendment means the federal requirement would not go away. Instead, the bill would simply tell states to decide which benefits must be included for consumers to be able to use its new tax credits.

According to a health-policy specialist who has been studying the change, as well as Republican congressional aides, the effect could be that insurers might have to comply with two different sets of benefits requirements.

“It’s creating an utter mess because there will be federal rules, which will govern everything else, and state rules in tax credits,” said Tim Jost, a health policy expert who has supported the Affordable Care Act. Insurers “are not going to know what to do.”

One industry official, speaking on the condition of anonymity because of the uncertainty ahead of Friday afternoon’s House vote, said that “any time you create a market where there are different sets of rules and different insurance products are treated differently, it really creates potential for instability . . . We are obviously concerned about that.

In addition, “the time frame does not appear to be realistic,” the official said, noting that the bill would have the new rules start next year — too soon for new federal regulations to be written, for state legislatures to adopt benefits standards or for health plans to take the changes into account in setting their prices for 2018.

Lauren Aronson, spokeswoman for the House Ways and Means Committee, confirmed in an email that language in the legislation “relates only to tax credits — not the rest of the individual market. Those insurance requirements remain in place.”

By tying the states’ role in defining health benefits to the bill’s tax credits, House leaders were looking ahead to the Senate, a congressional GOP aide said. Lawmakers there would need to handle the bill in accordance with the specific budget process being used, which would allow the legislation to pass by a simply majority vote.

White House officials and House GOP leaders have seen changes to the essential benefits rules as crucial to securing enough conservatives’ vote to pass the bill. Rep. Steve King (R-Iowa), for example, switched his position from nay to aye on Thursday after President Trump personally assured him that not only would the Senate strip those requirements from the legislation but also that the White House would do everything within its power to pass the measure in that form.

“I’m confident that the president will use his bully pulpit to make sure we get the 51 votes necessary,” King said in a Facebook video announcing his position. “In the end, we have the best chance to get a package that is the closest thing to the full repeal that we can get in this political environment.”

The fact that the essential benefits shift is more modest than many lawmakers initially thought underscores the frenetic pace as House Republicans have drafted and revised language over the past week.

Speaking to reporters Thursday, House Freedom Caucus Chairman Mark Meadows (R-N.C.) — who opposes the bill but has been one of the lead negotiators with party leaders on it — said he and other members were still trying to decipher the impact of last-minute changes to the measure.

When the question arose as to whether one tweak would make some veterans ineligible for tax credits, he noted, “Well, we’re not sure of those answers.”