As head of McDonald’s restaurants in his native France in the late 1990s, Mr. Hennequin had searched for ways to make fast food more appealing to a nation that prefers slow-simmered cassoulets and likes to savor a meal.

“To make McDonald’s and a Big Mac work in the country of slow food, we felt we had to pay more attention to space and showcasing,” said Mr. Hennequin, seated in front of zebra print wallpaper in one of the remodeled London restaurants.

He was right. After refurbishment, on average, sales increased 4.5 percent at the upgraded restaurants in France. The new outlets were so successful that two years ago Mr. Hennequin was asked to do the same for the rest of Europe.

But now the success of his makeovers comes with a challenge of its own: How much can you upgrade the image before McDonald’s isn’t McDonald’s anymore? “If you stretch the brand too much it can snap,” said Dean Crutchfield, director of marketing at the brand consultancy Wolff Olins in New York.

Image A McDonalds in central London includes chairs that are not typically found in the chains restaurants in the United States. Credit... Steve Forrest for The New York Times

Mr. Hennequin said he did not have a choice. “Reimaging is essential in the competitive world of retail,” he said. “We need to avoid aging faster than our customers.”

To do that he instructed the design studio he had set up in Paris to come up with nine different designs. Franchised restaurants, which account for about 64 percent of all European outlets, can then choose the design most appropriate for their location and clientele.