You can change the default VAT/GST/Sales tax settings for an individual forecast at any time.
Go to Forecasts, then open the forecast.
Select Controls, then Settings.
From here, you can update:
Whether the organisation is registered for VAT/GST/Sales tax
The VAT/GST/Sales tax scheme
The VAT/GST/Sales tax control account
The VAT/GST/Sales tax reporting frequency
The VAT/GST/Sales tax period end
The default VAT/GST/Sales tax rate
The default VAT/GST/Sales tax payment terms
Any changes apply only to the current forecast and any new predictions you create within it.