Jennifer Houghton clung to the banister in her Dallas mansion. Suspended about 10 feet off the ground, she braced her foot against the wall, extended her arm and placed an oversize pink-and-white ornament atop a spinning Christmas tree festooned with candied pink poinsettias.  Below her, a life-size Nutcracker stood sentry in the double-height foyer, which Ms. Houghton, 54, had reimagined as the Land of Sweets, with pastel-colored candy covering the railing and plush ice-cream cones hanging from the chandelier. “Freaking amazing,” she said, satisfied with the finished product.  In the kitchen, a candy-cane conveyor belt was perched on the counter. The front yard had been transformed into a Christmas tree farm with more than…