CESM1.2.0 provides 3 specified dynamics (SD) component sets for running with nudged meteorological fields. FSDW is the comset for SD-WACCM. It supports GEOS5 and MERRA analysis data. We do not support ECMWF. If you would like to do that, I would suggest starting with the FSDW compset, getting the GEOS5 meteorological fields used for that, and making sure you have ECMWF data that is in the same format. You may not need to modify the codes.