Would it be possible to track if the user copy something with the
mouse -> do a meta-command that look up what was copied and if there
is actually tabs in the buffer it will replace the spaces with tabs
When selecting text by dragging the mouse you are in a graphical
environment, in X, and while dragging the mouse X is talking to
the terminal, the graphical terminal, to obtain the text that is
being selected. There is no communication between X and nano,
nano has no knowledge of what you are doing with the mouse.
(And when you use --mouse, then you cannot select text with the
mouse. Nano consumes the clicks.)
So no, it's not possible to let nano modify text selections that
you make with the mouse under X.
Benno