The 38-year-old was granted dispensation to play against Prebbleton last weekend, with the sub union executive approving an application from Carter’s management team earlier this season.
Usually players must have made two regular season appearances to be eligible for the playoffs but the board can grant exemptions.
Carter played his first game of rugby in New Zealand since 2015 when Southbridge beat West Melton on July 4 - a match that served as a tune-up for his stint at the Blues.
Southbridge and Waihora have set up a Coleman Shield final thriller on Saturday with tight hard fought semi-final wins at the weekend.
Carter’s surprise addition to the Southbridge side proved decisive when he kicked five conversions and scored a try in the narrow 42-39 win over Prebbleton.
Southbridge’s final side for the final will be named after training on Thursday.
Harry Kirk scored a try and kicked a conversion and penalty in the win.
