In addition to the World Cup in the United Arab Emirates and tours of Bangladesh and Pakistan, New Zealand also have a Test series in India with that squad to be named next month.
New Zealand Cricket chief executive David White said changing times demanded changing strategies, with player welfare and support one of professional sport's biggest challenges, particularly in the current pandemic environment.
"The need to safeguard the well-being of our players and support staff is now very real, and we've endeavoured to do this by carefully managing their workloads over this (year's) massive playing programme," White said.
New Zealand players involved in this year's prematurely suspended Indian Premier League would be allowed to re-join their franchises when it re-starts in September.
"It's a pragmatic approach. We've always tried to be realistic about the IPL and this particular issue is very much a one-off, caused by a unique set of circumstances," White said.
Tom Latham will captain the side in Bangladesh and Pakistan with Williamson linking up for the Twenty20I World Cup which starts on 17 October in the UAE.
Ross Taylor was initially selected for the three one-day internationals in Pakistan but, with the brief nature of the one-week series and the length of quarantine protocols, it was decided he would remain in New Zealand to prepare for the Indian Test tour.
New Zealand squad for T20I series in Bangladesh
Tom Latham (capt), Finn Allen, Hamish Bennett, Tom Blundell, Doug Bracewell, Colin de Grandhomme, Jacob Duffy, Scott Kuggeleijn, Cole McConchie, Henry Nicholls, Ajaz Patel, Rachin Ravindra, Ben Sears, Blair Tickner and Will Young.