There was no scope under current immigration instructions to deny them a visa, Mr Stevens said.
However, immigration officers have been told they have the discretion to grant a character waiver in cases where it would be "unduly harsh" to decline a visa.
The changes are part of the agency's efforts to make sure that undesirable migrants and visitors do not enter or remain in New Zealand.
Last year, nearly 1200 people were prevented from boarding New Zealand-bound aircraft due to concerns.
Steve Stuart, Immigration's intelligence, risk and integrity general manager, said the implementation of border protection strategies including the introduction of "advance passenger processing" had helped reduce the number of "inadmissible" migrants.
"An increase in the number of passenger arrivals over the last five to 10 years has been matched by a decline in the number of inadmissible passengers arriving," Mr Stuart said.
In 2007, 1328 people were turned away at the border, but that number declined to 858 in 2010, and 684 last year.
Plans are also under way to make airlines accountable for the passengers they bring to the country.