It’s not unusual for a chef like Mr. Chang to parlay cooking talent and charisma into restaurants, cookbooks and television shows — a formula pioneered by the likes of Emeril Lagasse, Bobby Flay and Rick Bayless in the 1990s. But chef-driven food brands of the scope and ambition that Mr. Chang and Ms. Mariscal envision for Momofuku, with dozens of locations and mainstream packaged food products, are harder to pull off.

Adding to the challenge is Momofuku’s particular identity, which revolves less around a distinct culinary tradition than an attitude of restless innovation, boundary pushing and spontaneity. A formulaic chain of steakhouses, Momofuku ain’t. Scaling that ethos requires a tightrope act: Create enough structure and continuity to stave off chaos, without destroying the brand’s animating spirit in the process.

This suits Ms. Mariscal, a self-proclaimed control freak who does crossword puzzles to unwind, just fine. Colleagues say that she and Mr. Chang are alike in their relentlessly high standards. He’ll dress down a chef if items in the walk-in refrigerator aren’t all film-wrapped in a uniform way; she’ll notice if a piece of artwork is hung millimeters off true.

Momofuku employees have long looked to Ms. Mariscal as a barometer for what is right for the brand, with an uncanny touch for channeling Mr. Chang’s values and predilections. “Her intuition is almost infallible,” said Su Wong Ruiz, the general manager of Momofuku Ko, a branch with two Michelin stars. Recently, the company found itself in an ugly news cycle, when Mr. Chang publicly pleaded with his largest investor, Stephen Ross, to cancel a fund-raiser for President Donald Trump. With talk of a boycott circulating on Twitter, Momofuku decided to donate one day’s profits to charities including Planned Parenthood and Sierra Club. It was Ms. Mariscal’s idea.

She has demonstrated a particular knack for guiding the company’s growth — teasing apart which aspects of its early identity are core to Momofuku’s appeal, and which should be left behind to allow the company to evolve.

Take open kitchens. Mr. Chang’s restaurants were among the first to break down the barrier between cook and diner with kitchens that were visible from the dining room. This remains a feature of every Momofuku location to date. Yet Ms. Mariscal has waged an all-out campaign against backless stools — hallmarks of the company’s early thrift — which she sees as needlessly uncomfortable, and they have all but disappeared from the newer ventures.