imgdisplay and dsplot support the definition of one or multiple regions on displayed images (please consult the respective documentation if you are not familiar with this feature). When dealing with more than one EPIC event file, the region specifications can only be propagated to the OGIP spectral product generation. Therefore, the EPIC mosaic image generated by multixmmselect should be used only to define the source and background regions that will be propagated to multiespecget through the OGIP spectral product button.