I see now why you're asking. What he's thinking of doing is a bit risky from INZ's point of view. INZ need to get the feeling that he's found himself employment that can go on into the future. If your husband resigns and gets another skilled job, while his ITA has the skilled job counting in his application, it needs to be a permanent position, or one with a definite term of more than 12 months, or similar. (See SM7.15 b, here.
http://www.immigration.govt.nz/opsmanual/30549.htm) If he was to move jobs while the application was being processed, he'd need to be very careful ONLY to move to another job that was equally skilled, and that it was offered for the qualifying length of time. Also, he should be sure not to have any periods when he is not employed. He could still have some very searching questions to face up to.
In theory, if somebody has already been working in a skilled job for three months or more during the processing of their application when their Residence is granted, they shouldn't need to get a Section 49(1) condition on it, but in practice, we've heard on the forum of several people who nevertheless DID have this condition, that they had to work at least a further three months in the job to get their Residence free and clear.