Hi Georg,
I thought that I had 'found a solution', but now I am not so sure.
Select the image that you want to 'copy the FITS header information from'. Use the View FITS Header process icon to view the data. Save a copy of this process instance on the workspace. Pick a new image. 'Apply' the saved process icon 'to' the new image. Job done.
Well, 'somehow' I managed to get it to work, just once (I think), but I haven't been able to duplicate things.
Someone like Juan - with access to the code itself - needs to tell us if my suggestion 'could have worked', and then we have to decide, if not, whether this would be a useable 'user interface'.
Cheers,