Mammalian cells are the host of choice for the production of the majority of proteins with therapeutic value, especially those which need post-translational modifications. The current methods for stable cell lines generation rely on random integration of the transgene, which poses severe limitations to the efficiency, time and cost-effectiveness of the process. Hybridomas, a fusion of primary mouse B cells and myelomas, are stable, rapidly proliferating cell lines widely utilised for monoclonal antibody screening and production. The antibody specificity of a hybridoma clone is determined by the immunoglobulin sequence of the primary B cell partner. Here we report a platform for rapid reprogramming of hybridoma antibody specificity by immunogenomic engineering. We used CRISPR-Cas9 to generate targeted double-stranded breaks in immunoglobulin loci. Multiplexed-targeting enabled deletion of the native variable light chain and homology directed repair allowed replacement of the endogenous variable heavy chain with a fluorescent reporter protein, mRuby. New antibody genes were then introduced by using Cas9 to target mRuby and promote replacement with a donor construct encoding a light chain and a variable heavy chain, resulting in full-length antibody expression from the native immunoglobulin heavy chain locus. Since hybridomas surface express and secrete antibodies, reprogrammed cells were isolated using flow cytometry and cell culture supernatant was used for antibody production. The simplicity of the approach was exemplified when a homogenous population of antibody-producing hybridoma cells was generated using only a single transfection and screening step.