If you create a desktop shortcut to a command or application, you cannot
edit it after it is created (as far as I can tell).  The rightclick ->
properties dialog box has things like emblems, icons and permissions, but
no way to adjust the command line.

To duplicate:
 - right click on the desktop, choose new launcher
 - create a launcher for [someapp]
 - click ok to finish 

 - now try to edit the command line (for example, to add a flag)
 - the logical place for this is rightclick->properties, but there is no
way that I can see to edit this information.  

To me the logical place to edit the information you created with 'create
launcher' (name, generic name, comment, command, type) is the 'basic' tab
in the properties box.  You already have Name in there, why not put the
rest of the information.  Nautilus looses usefulness if you have to
recreate shortcuts every time you need to edit them.