There's no threshold if you are either importing or manufacturing exciseable goods. However if you are stocking exciseable goods and your stock in hand is more than a prescribed limit, the you would be obliged to charge excise tax on the excess stock.

This means that if you are an importer or manufacturer, you should be registered for excise tax. But you would be obliged to register as a stock piler only if you have some excess stock with you on the date of introducing the excise tax. Generally hotels, restaurants, shopping malls etc would qualify as a stock piler.