Moles' resignation was signalled earlier in the week when a report was leaked to the media which indicated the players had lost confidence in the former Warwickshire opening batsman.
But the Black Caps wicketkeeper-batsman's demotion came as a surprise.
However, it appears to be a symbolic gesture.
New Zealand Cricket (NZC) chief executive Justin Vaughan told the Otago Daily Times McCullum would take over the captaincy if Daniel Vettori was unable to continue.
"I still believe the intention is, in the event of Daniel being injured, Brendon will step in as captain, so in that regard that hasn't changed," Vaughan said.
By relieving McCullum of the vice-captaincy, the selectors hope he will get on with the job of scoring runs at the top of the order.
"And also they wanted to send a signal to the other senior players that they want them to step up to the mark as well."
The Otago player was thrust into the limelight when it was revealed six leading players had delayed signing their NZC contracts until they knew how much of the Indian Premier League they would miss.
Asked if the decision to demote McCullum was related, Vaughan said there was no connection.
"This is just a standard selection decision . . . end of story and certainly nothing to do with any issue Brendon has with NZC or anything of that nature."
McCullum refused to talk to the Otago Daily Times but told the Herald on Sunday he was disappointed.
"It's disappointing, obviously, in many respects, but the fact is I can now concentrate on my roles of scoring runs and keeping wickets.
"I still have some fairly big goals I want to achieve for New Zealand, including the captaincy, and this has not changed that."
Vaughan said while all the changes had been unsettling before the limited-overs series against Pakistan in the United Arab Emirates, the Black Caps were well-placed to build on the recent success of reaching the final of the Champions Trophy.
"Let's not forget they have come off a fantastic performance in South Africa . . .
The fact there won't be a head coach puts the acid on the senior players, which I think is a good thing.
They're going to have to be self-reliant over there and . . . let's hope all those things result in producing the goods."
The future for Moles is not so rosy.
He was effectively forced to stand down less than a year into a three-year contract when negative feedback from some of the senior players left his position untenable.
He admitted finding another job at the elite level of the game would be difficult.
