$guests = Import-Csv -Path C:Usersshant_000DesktopUploadGuest_test.csv
$output = gc '.Sample Json.json' | ConvertFrom-Json
$array = New-Object System.Collections.ArrayList;

foreach ($g in $guests) {
    $array.Add($output);
    $a = $array[$array.Count-1];

    $a.Username = $g.'EmailAddress';
    $a.DisplayName = $g.'FirstName' + ' ' + $g.'LastName';
    $a.Password = $g.'LastName' + '123';
    $a.Email = $g.'EmailAddress';

    foreach ($i in $a.ProfileProperties.Count) {
        $j = $i - 1;

        $prop = $a.ProfileProperties[$j];

        if ($prop.PropertyName -eq "FirstName") {
            $prop.PropertyValue = $g.'FirstName';
        } elseif ($prop.PropertyName -eq "LastName") {
            $prop.PropertyValue = $g.'LastName';
        }

        $a.ProfileProperties[$j] = $prop;
    }

    $array[$array.Count-1] = $a;
}

$array;

$jsontext = gc '.Sample Json.json'
..........
foreach ($g in $guests) {
    $a = $jsontext | ConvertFrom-Json

    # process $a
    # ............

    $array.Add($a) >$null
}

foreach ($g in $guests) {
    $a = $output.PSObject.Copy()
    # ............

    $a.ProfileProperties = $a.ProfileProperties.PSObject.Copy()
    # ............
    foreach ($i in $a.ProfileProperties.Count) {
        # ............
        $prop = $a.ProfileProperties[$j].PSObject.Copy();
        # ............
    }

    $array.Add($a) >$null
}

bar

$o1

$json = Get-Content '.Sample Json.json' -Raw
$array = foreach ($g in $guests) {
    $a = $json | ConvertFrom-Json   # create new object

    $a.Username = $g.'EmailAddress'
    ...

    $a   # echo object, so it can be collected in $array
}

$json = Get-Content '.Sample Json.json' -Raw
$array = foreach ($g in $guests) {
    $a = $json | ConvertFrom-Json   # create new object

    $a.Username = $g.'EmailAddress'
    ...

    $a   # echo object, so it can be collected in $array
}