We did chat and Jim convinced me that this particular task shouldn't load any other datasets. So galactic extinction will get applied later.
This task is just taking advantage of the fact that the WCS, PhotoCalib, PSF, VisitInfo etc... is already in memory and extracting what we need from it so that we don't have to fetch it all from disk again to do the transform. I CAN envision these as plugins, but I think this your task will do the trick as-is.
Looks good. Remember that the config doEvalLocCalibration IS the part that people will write a lot and usually from memory. I have to run, and will think about, what abbreviation I would type to doEvaluateLocalCalib