Need to popluate hidden Active Directory attrributes from all users

There is already a powershell script written that needs some tweaking based on the values you want to update.  You'll need to understand that powershell is pulling in the column names as variables and setting the values in the rows beneath.  In your case you would want to update the CSV to include the AD ID and edit the script to update based on ID rather than mass update on an OU such as this one.

It's a good start though for what you're looking for and an excellent example to begin with.

https://gallery.technet.microsoft.com/scriptcenter/PowerShell-script-to-376e9462

It's not rocket science with PowerShell (2008 R2 or later); the import file aside, it's a one-liner.
You'll need a csv like this:

SamAccountName, employeeID, roomNumber
jdoe, 1234, 42

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The 'Import-Module ActiveDirectory' is only required if you're still running PS 2.0; PS 3.0 or later will load the module automatically:

Import-Module ActiveDirectory
Import-Csv C:\Temp\userlist.csv | % {Set-ADUser -Identity $_.SamAccountName -Replace @{'employeeID' = $_.employeeID; 'roomNumber' = $_.roomNumber}}

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