Get-ExchangeCertificat
Select Thumprint
$txtrequest = Get-ExchangeCertificate -Thumbprint N° du Thumprint | New-ExchangeCertificate -GenerateRequest
[System.IO.File]::WriteAllBytes('\\192.168.xxx.xxx\xxx\ContosoCertRenewal.req', [System.Text.Encoding]::Unicode.GetBytes($txtrequest))
puis
Import-ExchangeCertificate -FileData ([System.IO.File]::ReadAllBytes('\\192.168.xxx.xxx\cert\xxxxx.crt'))