Methods and compositions for rapidly replacing cMyBP-C in sarcomeres featuring the creation of Spy-C mice, which are mice genetically engineered to express cMyBP-C with a protease recognition site and SpyTag peptide introduced into the cMyBP-C gene. In permeabilized myocytes from the Spy-C mice, the cMyBP-C protein can be cleaved at the protease recognition site, and the N-Terminus of cMyBP-C can be removed while the C-terminus remains anchored to the thick filament. A new peptide featuring the SpyCatcher sequence can be covalently bonded to the remaining portion of cMyBP-C, thereby creating a modified cMyBP-C protein. The methods and compositions of the present invention allow for the reconstitution of full-length cMyBP-C at the precise position of native cMyBP-C in the sarcomere and allow for a variety of modifications to be introduced to cMyBP-C in situ.