functions/Add-MemberOrSetValue.ps1

function Add-MemberOrSetValue{
    [cmdletbinding()]
    param(
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [object]$InputObject,
        [Parameter(Mandatory = $true)]
        [string]$PropertyName,
        [Parameter(Mandatory = $true)]
        [object]$PropertyValue
    )

    process{
        if(-not (Get-Member -InputObject $InputObject -name $PropertyName -Membertype Properties)){
            $InputObject | Add-Member -NotePropertyName $PropertyName -NotePropertyValue $PropertyValue
        }
        else{
            $InputObject."$PropertyName" = $PropertyValue
        }
    }
}