$str = 'CN=Admin-Lastame\, Paul,OU=Users,OU=Data_Admins,OU=Admins'
#$str
[string[]]$a = $str.Replace('\,', '~~~').Split(',')
#$a
#$a.Count

for ($i=0; $i -lt $a.Count; $i++)
{
    $a[$i] = $a[$i].Replace('~~~',',')
}

$a

$cn = 'CN=Admin-Lastame\, Paul,OU=Users,OU=Data_Admins,OU=Admins,DC=....'
$pat = 'CN=\w+\-(\w+)\\,\s+(\w+),.*$'
[regex]::Replace($cn, $pat, '$2 $1')

Paul Lastame

$pat = 'CN=Admin-(\w.+)\\, (\w+),.*$'