On: New Features in the Fish Shell

[shakna]

Or even more simplified:

    funced foo
    funcsave foo

funced will either allow you to edit it inline, with a clever multiline system, or through your $EDITOR.

funcsave will record the file to the place you want once you're happy with the changes.

Which means you can funced as many times as you want on both new and old alike until you're happy with the function.