A method to modify mammographic images so that they appear as if acquired with different radiographic factors has been developed for use in virtual clinical trials. The methodology was validated using a custom-made 3D printed breast phantom. The radiographic output, 1st half value layer, noise coefficients, grid factor, glare and scatter-to-primary ratio were measured on a GE Senographe Essential digital mammography system. Three images of the phantom at each of four dose levels were acquired with a Mo/Mo 26 kV spectrum using the same digital mammography system. In addition, three images were acquired at each of 24 kV and 28 kV. High dose images at 26 kV were modified to simulate the ones acquired at a lower dose, and at the lower and higher tube voltage. The signal level was changed to account for different dose level, scatter, grid attenuation and change of signal across the image. Noise was then added to the image to match the expected noise for the target image. The power spectra of the target and the simulated images were calculated and compared. This showed that they match to within an average difference of 4%. Also, an average structural similarity index of 0.998 was obtained, meaning that the images are almost equivalent. Using breast phantom images, it was shown that this method can replicate images as if acquired with different radiographic factors. Images modified in this manner could be used for clinical evaluation of image quality or for other types of virtual or human observer studies.