It would be nice to have a variant of the ALTER TABLE statement,
similar to the SET INCREMENT BY or SET RESTART WITH variants,
that allowed a user to change the CYCLE option on an IDENTITY column.
I think that the code flow for this could be closely modelled on the
code flow for the SET INCREMENT BY variant: after the statement
is parsed, we simply need to drop and recreate the underlying SEQUENCE
object with the desired CYCLE option (and preserving all the other
aspects of the underlying SEQUENCE object.