Why do I get a "command not found" error when trying to run one of the Montage modules?
If you are trying to run the command from the same directory as the executable (i.e., Montage_vX.Y/bin), make sure that your path contains "."
If you are trying to run the command from another directory, add Montage_vX.Y/bin to your path.
Is there a way to look at or edit FITS headers?
The Montage package includes the WCS library and tools, including a program called "edhead." This is not built automatically when you build Montage; if you want to compile it, go into Montage_vX.Y/lib/src/wcstools-3.5.2 and type "make edhead". This will create an executable edhead in this directory. If you want to be able to call it from anyplace, you should copy it into a directory that is included in your path.
To run edhead, simply type edhead filename.fits. It will strip the header from the FITS file and open it for editing using the program defined in your environment. Make the changes, save and exit the editor, and the header is re-attached to the image.