Between November 2006 and August, Mozilo changed the plans outlining how many of his shares would be sold monthly, the Los Angeles Times reported.
Mozilo unloaded 4.9 million Countrywide shares, most of which he bought through exercising options.
Hundreds of executives use similar trading plans, approved by federal regulators in 2000 as a way to defend against insider trading allegations. While not illegal, it is highly unusual for the plans to be changed so often in a short period, experts said.
"If a guy is changing his plan around, I would think that would send up a red flag. I wouldn't allow my clients to do it," said Thom F. Carroll, a financial planner with the Baltimore wealth management firm Carroll, Frank & Plotkin.
Mozilo adopted a new trading plan, added a second one and then revised it while the housing and mortgage industry slumped, the Times reported, citing regulatory findings.
The changes allowed him to sell hundreds of thousands of additional shares before Countrywide stock plunged.
Sandy Samuels, Countrywide's chief legal officer, said Mozilo's stock sales were all "in accordance with company policy."
"The (trading) plans were put into place in consultation with Mr. Mozilo's financial adviser, without regard to any non-public or market information," Samuels said in a prepared statement to the Times.
Calabasas-based Countrywide, the nation's largest mortgage lender in terms of volume, faces a lawsuit claiming it failed to warn employees about the depth of its financial troubles, resulting in heavy stock losses in their 401k retirement accounts.
The company recently said it will eliminate as many as 12,000 jobs in the coming months. Its stock, meanwhile, is off more than 50 percent from its $45.03 high on Feb. 2.