vCenter does not have an in-built mechanism to export and import Global Permissions.
In this post, I will describe a script that I have written - globalPermissionManager.py - that performs this export/import operations for Global Permissions.
What is globalPermissionManager.py ?
The script is available on my GitHub here.
The script is used to export ALL Global Permissions from a vCenter Server Appliance to an object file, and then re-import them as needed. The primary use case for this, that I use it for is : Cross Domain Repoints to a new SSO.
William Lam has a PowerCLI script which contains two functions New-GlobalPermission and Remove-GlobalPermission, if we need to interact with global permissions using PowerCLI : https://williamlam.com/2017/03/automating-vsphere-global-permissions-with-powercli.html
However, in my experience, having a python script that just handles everything for you and requires no input for individual users or groups, is a lot more convenient. The script uses the same underlying API as the PowerCLI script created by William Lam.