Save the file to your desktop (or place of choice) right click on it, select open with and specify the program.
Now go back to Evolution, and you will see the change is picked up there. They share the mime type associations.
That is how I thought it should work, but it apparently it doesnt on this installation.....
so, I am modifying my question to :
Where is the definition file for Nautilus (system-wide) Mime-Types?
I seem to have a bunch of cruft in there (wherever it is) already that I would also like to remove...
TIA
WPH