A strategy of altering the modulation type and frequency of commercial continuous wave ESR spectrometers without changes in the main console is discussed. A simple converter unit, permitting the use of various external receivers, widening the possibilities for the basic commercial set-up is suggested. Block diagrams for altering the modulation frequency and type are presented and the use of boxcar averaging systems for the time-resolved experiments is discussed in detail. As an example of a successful application of this method, some results obtained with two different RYDMR accessories, based on the commercial CW ESR spectrometers, are discussed. X-band OD ESR studies of hydrocarbon solutions are illustrated by the spectra of p-xylene and trans-phenyl-propene radical cations, and methyl acrylate and trans-azabenzene radical ions, detected in situ under X-irradiation. Semiconductor studies are illustrated by CW and time-resolved X-band ODMR spectra of PGa-P3Y point defects as well as its OD ENDOR and ENDOR-induced ODMR spectra