My demand forecasting solution generates point forecasts and forecast intervals for millions of time series (# of products × # stores for a large retailer) using statistical models.
Business users (i.e. with no stats knowledge) can go in an adjust some of those forecasts based on their experience and business plans. When they do so, they only adjust the point forecast (typically for a few thousand forecasts out of the 2~3 million that are generated each week).
How can the forecast intervals be calculated for the user adjusted forecasts?