This script can be used for changing the UPN of multiple users based on a CSV File.
Before starting, Please ensure that the following values are properly updated.
1) $oldSuffix = 'insideactivedirectory.com' [Your Current UPN]
2) $newSuffix = 'insidevirtualization.com' [Proposed new UPN]
3) Input File Name - userlist.csv
Input file should be a CSV file with loginid as the header and each line containing one samaccountname.
Please test the script with a small user base first always.
Active Directory Module should be installed and should import the module if required.