If you need to change your SharePoint 2010 Farm's Passphrase, it's definitely doable. A farm passphrase is created when running PSConfig and when joining new servers to the farm. If you inherit a SharePoint farm from someone else and they have forgotten the passphrase (or they left the company), you can always reset the passphrase. You are going to use SharePoint Management Shell (PowerShell) to make this quick and easy change. Here is what you will enter into PowerShell:
$passphrase = ConvertTo-SecureString -asPlainText -Force
PowerShell will then ask you what the new passphrase is going to be....
Once you have that typed in, you will need to enter another line into PowerShell:
Set-SPPassPhrase -PassPhrase $passphrase -Confirm
You will need to confirm the passphrase you entered before. Click Y to confirm this change. Now your farm's passphrase is updated!