It would be convienent to modify the internal x y coordinates of a geotif.
Sometimes imagery just needs to be shifted rather than reprojected, and the ability to modify the interal georeferencing would make this possible. I was able to do this in Erdas Imagine years ago, but discovered it is not possible using ESRI software. Geotif Examiner by Mentor Software allowed you to do this by transfering coordinates from a tif world file into the geotif (one image at a time), so it can be done with a simple free program.
My current work around is create tif world files with the desired shift, and to use a program like irfanview to batch copy the imagery to a new location. The copy process strips out the internal georeferencing and produces a simple tif, but it also drops off the fourth band (NIR) in the process. I then place the modified tif world files in the same folder, then use a model with iterate rasters to define the projection of all the rasters. It works but I end up with two copies of the data and one of which is missing the fourth band. Thanks