The Environment Court confirmed that it has jurisdiction (through section 269 of the RMA) to allow further submissions after the close of a hearing but before the decision, but it declined to allow it in Britten v Auckland Council  NZEnvC 205.
The Court commented that leave should be granted sparingly, and there should be no significant prejudice. One party should not be permitted to effectively reopen the debate after the evidence and submissions have concluded without there being very compelling reasons to do so, and without reason for the failure to raise it during the hearing being explained.
The Court noted that leave is unlikely to be granted in many cases as the case management proceedings in the Court allow the parties plenty of time before a hearing to outline the nature of their cases and to consider the legal principles that might apply.
Bell Gully also observes that at a Council level, Hearing Commissioners have the same powers as the District Court with regard to regulating and conducting a hearing (see section 41(1)(a) of the RMA; and section 4(1) of the Commissions of Inquiry Act 1908) and that they can also re-open a hearing (after closing but before decision) pursuant to the District Court Rules (i.e. DCR 12.6.6 which applies HCR 10.10).