Along with new England skipper Ben Stokes and a new managing director in Rob Key, McCullum has been charged with turning around a team that has managed one win in 17 tests.
Stead said McCullum, along with former Black Caps head coach Mike Hesson, had been the catalyst for change in New Zealand cricket and would waste little time making his mark in his new role.
“I have no doubt, knowing Baz (McCullum), that he will have an instant impact,” said Stead.
“Brendon will bring that heart-on-the-sleeve type (of) play, I’m sure, into that England squad.
“He’ll be really clear on what he wants and how he wants them to play the game.
“(But) … it’s still about the players playing the game. I’m sure he will have some impact but whether that’s right now or in the future, who knows?”
New Zealand named a 15-man squad on Monday but injured batsman Henry Nicholls and pace spearhead Trent Boult, who played in the Indian Premier League final at the weekend, are unlikely to feature at Lord’s.
Winners of the World Test Championship last year, New Zealand’s title defence is on shaky ground after tying home series against South Africa and Bangladesh.
They are also a different lineup from the side that beat England 1-0 last year, with senior batsman Ross Taylor and wicketkeeper BJ Watling having retired.
Stead said his team did not see themselves as favourites to win the series.
“We certainly don’t look at it that way. (It’s) a 50 percent chance for both teams of winning the game when you start.
“It’s just winning small moments and then the result will look after itself.”