You can use the 'Backup-AREncryptionKey' PowerShell cmdlet to create a new backup file of the encryption key. This allows you to replace an existing backup file with one using a new password, or to create a new backup file in case you've lost your existing backup file.
NAME
Backup-AREncryptionKey
SYNTAX
Backup-AREncryptionKey [-BackupFile <string>] [-DatabaseCredential <PSCredential>] [-DatabaseName <string>] [-DatabaseServer <string>] [-ExecuteAs <PSCredential>] [-Password <SecureString>] [-ValidateOnly] [<CommonParameters>]
EXAMPLE
Creates a file that stores a copy of the current encryption key used in the configuration database of the local Administration Service instance.
-------------------------- EXAMPLE 1 --------------------------
C:\PS>$pwd = read-host -AsSecureString -Prompt "Password"
C:\PS>Backup-AREncryptionKey -BackupFile "c:\temp\AREncryptionKey.bin" -Password $pwd