I don’t want to say that Tex-Mex cuisine resists change. I think, to paraphrase Charles Bukowski, Tex-Mex just feels better when change is not around.

Perhaps I should clarify. Tex-Mex, by definition, has constantly adapted to its environment and the people who populate it. Change is built into the term. At the same time, Tex-Mex means different things to different people. To chef Adán Medrano, author of the terrific “Truly Texas Mexican,” Tex-Mex cooking has been an ever-evolving confluence of Mexican, European and indigenous Texas ingredients and techniques, the border between Mexico and America nonexistent to the people who developed this cuisine over centuries.

But for countless Texans who came of age in the 20th century, Tex-Mex is something more artificial. It is a bastardization of Mexican cooking that caters to white American diners who, at one time or another, were largely indifferent to the flavors found south of the border. It gladly embraces lard, processed cheese and the deep fryer for those U-shaped taco shells. To many, like me, this form of Tex-Mex is comfort food, even in an era when we’re supposed to crave authenticity (whatever that means).

Bastardized Tex-Mex is easy to identify. It is budget-minded hedonism disguised as Mexican food, a hybrid cuisine hopelessly devoted to fat, salt and alcohol. Think Velveeta cheese. Thin brown gravies. Sizzling platters piled high with juicy fajita meat. Bottomless baskets of fried chips, ready to sink into tomato-heavy salsas. Glasses as large as hot tubs pumped full of slushy margaritas, their rims covered with enough salt to preserve a polar bear. Combination plates smothered in bubbling, lavalike processed cheese.

To change this style of Tex-Mex cooking — to improve it with quality ingredients or cheffy techniques — is, on some level, to misunderstand the cuisine itself. This Tex-Mex is defined by its American devotion to convenience and indulgence.

All of this helps explain why I was nervous when the Rincon family decided to hire chef Nathan Breedlove, an alum of José Andrés’s ThinkFoodGroup and Le Diplomate, and asked him to gussy up the Guapo’s experience for the tourists and boutique hounds who prowl Georgetown. Whatever you think of Guapo’s, the chain has always had a personality of its own. The late Hector Rincon, a native of Colombia, and his children engineered their own take on Tex-Mex, one that made room for lomo saltado, fried plantains, ropa vieja and other dishes from the Americas.

Working with sous chef Sergio Galindo and pastry chef Elisa Reyna, Breedlove wanted to reel in the sprawling menu — at least a little — and root the new Guapo’s of Georgetown more in Mexico. Predictably, the chefs faced resistance from family members who were not keen on radical change. I mean, with nearly 30 years of success with Guapo’s, who could blame them?

“Baby steps, that is what I’ve had to learn,” Breedlove tells me. “Just taking it little by little.”

The chefs had their biggest effect on the lunch menu, where you will find a selection of torta sandwiches and Mexican-style tacos, wrapped in corn tortillas prepared daily at a company facility in Manassas and shipped to the restaurant. The tacos are modest by Tex-Mex standards — they ditch the lettuce, shredded cheese and sour cream toppings — yet they don’t always trust that the classic preparations will appease the Georgetown palate. The beef tongue taco, for example, comes slathered with a toasted ancho chile sauce, which masks the offal’s full-on funk. The tortillas don’t help, either: They’re often stiff and aroma-free after their long journey from Northern Virginia.

Breedlove and crew, I think, succeed better when injecting new life into old Guapo’s recipes. Their methods are discreet, subtle, respectful.

They’ve jettisoned the zucchini in the vegetable fajitas and replaced them with meaty oyster mushrooms, each lightly charred to mimic the traditional strips of skirt steak. The kitchen also braises the shredded beef that’s rolled into the enchiladas, making for a more succulent filling beneath that melted layer of Monterey Jack and cheddar cheeses. Even the ranchera sauce on the enchiladas has been given a makeover: It relies on a mix of charred tomatoes, onions and jalapeños while dumping the thickeners found in the sauce at other Guapo’s locations. This is my idea of enchiladas supreme.

Among the handful of ceviches is a Peruvian-Japanese preparation created by Galindo, who once worked for Jean-Georges Vongerichten, a chef famous for his embrace of the Asian pantry. Galindo’s Nikkei ceviche relies on a fresh catch each day. My version was prepared with squares of tilapia, each one the color of black tea, courtesy of a marinade that combines citrusy Peruvian tiger’s milk with a reduction of soy sauce and orange juice. Served with chunks of pineapple, toasted chulpe corn, cilantro and more, the ceviche is a freeway pileup, not subtle but delicious.

Despite the promise — the threat? — of moving the center of gravity to locales deeper inside Mexico, this Guapo’s location still feels fundamentally part of the chain. The chips are still razor-thin and addictive. The salsa is still fresh, bright and watery. The tacos al carbon, wrapped in those buttery housemade flour tortillas, still make me unbelievably happy, even when the server forgets the accompanying plate of condiments. The server did ask me, though, how I wanted my steak cooked for the tacos. I believe that was a first.

The most jarring element about this restaurant, the trendiest of the Guapo’s family, is the location itself. Tucked into the plaza level of Washington Harbour, within misting distance of the dancing fountains, the restaurant sports an interior design that befits its high-rent neighborhood. You won’t find walls covered with bullhorns, neon Dos Equis signs, serapes, Talavera pottery, Spanish clay roof tiles or any other clumsy signifiers of Mexican American culture. The Georgetown-based firm Ernesto Santalla has stripped the room down to a minimalist statement. The chain’s twin border cultures are expressed mostly through colors, an earthen adobe or a patriotic red. It’s a stunning space.

It’s too bad the room doesn’t extend to the patio, where you are subjected to the Greek Revival luxury liner that is Washington Harbour. It’s outside that I must do the hard work of reconciling my love of humble Tex-Mex, even a pretty version of it, with this amusement park of conspicuous consumption. I’m not there yet.

If you go

Guapo's of Georgetown

3050 K St. NW, 202-844-5777, guaposrestaurant.com.

Hours: 11 a.m. to 10 p.m. Sunday through Thursday; 11 a.m. to midnight Fridays and Saturdays.

Nearest Metro: Foggy Bottom-GWU, with a 0.7-mile walk to the restaurant.

Prices: $5 to $15 for appetizers, soups and salads; $11 to $65 for ceviches, burritos, tacos, fajitas and combination plates.