powershellv2 - add new parameter to custom object - object

Question

I have created a custom Object using the code below, but I now need to add an additional property.
Reading the online documentation and help files suggests that I need to use add-member (as per my example below).
But When I run this I get:
Add-Member : A positional parameter cannot be found that accepts argument 'newvar'.
What is the correct syntax to add a new parameter to an Object.
Also, if I wanted to update a parameter with a different value, can I use the the same add-member? (there doesn't appear to be an 'update-member' cmdlet)
$TestList = #(
"item1"
"item2"
)
$TESTObject = #()
foreach($a in $TestList)
{
$dItem = $a
$TESTObject += New-Object PSObject -property #{
item = "$dItem";
}
}
FOREACH($a in $TESTObject)
{
#DO STUFF HERE
$newVar = 1234
$a | Add-Member newvar $newVar
}

Answer 1

The way I have found to do this is:
Add a member to a custom (PSObject) Object
Add-Member -InputObject $TESTObject -MemberType NoteProperty -Name newVar -Value $newVar
And to update an existing member I use
Add-Member -InputObject $TESTObject -MemberType NoteProperty -Name newVar -Value $newVar -force
whether this is the best way to do this (or even the correct way) I'm not sure. But it seems to work.