The limit of 256 users in a WhatsApp Group only applies when Admin is Manually adding Users. Therefore, you can add more than the limit people into a single WhatsApp chat group by sharing the invite link.
Steps to Increase Users in a WhatsApp Group
Tap and Open WhatsApp Group
Tap on the Group info from the menu
Tap on Invite to Group via Link
Share the Link with prospective user of the Group