A method for modulating double-strand break-induced mutagenesis at a genomic locus of interest in a cell, thereby giving new tools for genome engineering, including therapeutic applications and cell line engineering. A method for modulating double-strand break-induced mutagenesis, concerns the identification of effectors that modulate double-strand break-induced mutagenesis by use of interfering agents these agents are capable of modulating double-strand break-induced mutagenesis through their respective direct or indirect actions on said effectors. Methods of using these effectors, interfering agents and derivatives, respectively, by introducing them into a cell in order to modulate and more particularly to increase double-strand break-induced mutagenesis. Specific derivatives of identified effectors and interfering agents, vectors encoding them, compositions and kits comprising such derivatives for modulating or increasing double-strand break-induced mutagenesis.