If I put another 23 ft wire to the radio ground and run it off as
closely s possible to 180 degrees away from the first wire, will this
necessarily (likely?) improve reception?

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You will have an additional, elevated radial wire.

In some directions and elevation angles and frequencies reception will be
very slightly improved. In other directions and elevation angles and
frequencies reception will be very slightly worse. On the average, no
change.

By changing it to a centre-fed dipole, delete 'very slightly'.