We study coherent perfect absorption in organic microcavity resonators and extend these principles and our findings to more complex microresonator systems that, beyond absorption, also possess additional cavity energy dissipation mechanisms. The experimental approach uses laser interferometry to closely monitor the energy fluxes within the system at all device ports as a function of the device geometry and the phase relationships of the incident beams. A particular focus is on optical systems based on 2nd order Bragg gratings, which are crucial for the operation of organic distributed feedback (DFB) lasers or as light incouplers in optical waveguiding films. Coherent control allows the diffraction efficiency of the underlying grating to be tuned over a wide range of values. This strategy allows significant optimisation of resonator structures for high efficiency light coupling in optical waveguides and fine tuning of grating parameters for the most efficient optical mode conversion.