Get-ChildItem [12][09][0-9][0-9]-[01][0-9]-[0-3][0-9]_* -File -Recurse

|Rename-Item -Newname {'{0:dd-MMM-yyyy}_{1}' -f (Get-Date ($_.Name.Split('_')[0])),($_.Name.Split('_')[1])}

$_.Name.Split('_')