The merged events list has already been processed for bad pixels during pipeline processing. However there are cases when this automatic procedure (using badpixfind for PN and embadpixfind for MOS) does not work perfectly and the user may wish to improve on it, without regenerating his events lists from scratch (epchain and emchain take a long time to run).
If a single bad pixel is obvious in the data, it is possible to eliminate the corresponding events in evselect by testing CCDNR, RAWX and RAWY. Then the user must manually update the BADPIXnn extension (where nn = CCDNR) to ensure that eexpmap and arfgen will account for the new bad pixel. If there are several such bad pixels, this becomes quite tedious. ebadpixupdate proposes to do that for you.