How to append to powershell Hashtable value?

I am interating through a list of Microsoft.SqlServer.Management.Smo.Server objects and adding them to a hashtable like so:

$instances = Get-Content -Path .\Instances.txt
$scripts = @{}

foreach ($i in $instances)
{
    $instance = New-Object Microsoft.SqlServer.Management.Smo.Server $i
    foreach($login in $instance.Logins)
    {
        $scripts.Add($instance.Name, $login.Script())       
    }
}

So far so good. What I want to do now is append a string to the end of the hashtable value. So for an $instance I want to append a string to the hashtable value for that $instance. How would I do that? I have started with this, but I'm not sure if I'm on the right track:

foreach ($db in $instance.Databases)
{       
    foreach ($luser in $db.Users)
    {
        if(!$luser.IsSystemObject)
        {
            $scripts.Set_Item ($instance, <what do I add in here?>)
        }
    }
}

Cheers

$h= @{}

$h.add("Test", "Item")
$h

Name                           Value                                                                                                                                                   
----                           -----                                                                                                                                                   
Test                           Item                                                                                                                                                    

$h."Test" += " is changed"
$h

Name                           Value                                                                                                                                                   
----                           -----                                                                                                                                                   
Test                           Item is changed