You have always been able to discount time period fee, but not if that time period fee was a part of the fiscal year fee. Now you can discount the registration fee even if you are using the fiscal year time period configuration.
To make your fiscal year time period fee discountable go to Set Up/Terms. Choose Fiscal year you wish to make discountable and click the ellipsis to the right of that record. To make that fiscal year fee amount discountable, just check the discount checkbox and click the green checkmark to save the changes you just made.
Now, any time period fee that is under this fiscal year umbrella will be discountable. However, you can change this form term to term. For example, if your organization has four terms within one fiscal year, you can make one or two terms discountable and the rest non-discountable by just updating the discount check box.