PORT ST. LUCIE — The Mets are bringing back relief great John Franco as a guest pitching instructor for one week next month, then will use him in a marketing role and have him do some commentary work for SNY during the season. The club announced the move today. Franco, a Brooklyn native who spent 14 prolific years with the Mets before making something of a messy exit after the 2004 season, said he “felt the itch” after being out of the game for the past four years and would like to coach or manage eventually. Darryl Strawberry also is in camp again for a visit and some guest instruction.