Abstract: Dietary fiber (DF) modification has emerged as a crucial strategy for enhancing its functional value by precisely tailoring its molecular structure, physicochemical properties, and performance. This approach continues to attract growing interest in the fields of food science and nutrition due to its broad application potential. This review systematically examines the principal techniques for modifying DF—including physical, chemical, biological, and combined methods—and highlights recent advances in their application within food systems. It further synthesizes the effects of various modification strategies on the structural attributes, physicochemical properties, and functional behaviors of DF. The analysis indicates that appropriate modification methods can markedly improve the water-holding, oil-binding, swelling, and adsorption capacities of DF, while also enhancing functional properties such as antioxidant, hypoglycemic, and hypolipidemic activities. These improvements significantly broaden the potential applications of DF in a diverse range of health-promoting foods. Moving forward, research should prioritize the development of efficient and environmentally sustainable modification technologies, elucidate the structure–function relationships of modified DF, and establish standardized protocols for safety and efficacy evaluation. Such efforts will accelerate the innovative utilization of DF in high-value functional foods and precision nutrition.