I’m confused by what you are saying, are you trying to do this in the Deploy-Application.ps1?
As I think the linked article inferred this needs to be modified in the AppDeployToolkitMain.ps1
Edit: Ah!, You should have read a little further down the thread
…
Not:
$buttonContinue.Visibility = 'hidden'
but:
$buttonContinue.Visible = $false