MIAMI — As many states prepare to introduce a linchpin of the 2010 health care law — the insurance exchanges designed to make health care more affordable — a handful of others are taking the opposite tack: They are complicating enrollment efforts and limiting information about the new program. Chief among them is Florida, where Gov. Rick Scott and the Republican-dominated Legislature have made it more difficult for Floridians to obtain the cheapest insurance rates under the exchange and to get help from specially trained outreach counselors.