Can trial periods be ended early?

Yes, any customer's trial subscription can be removed from the trial period at any time by altering the trial end date. This is easily done by visiting the subscription's details page and within the subscription summary window, click on "Change Trial End Date" and set the time that you would like to remove the customer from the trial period. Please note that you can set this to any date and time in the future even the current day, but you cannot set it to a past date and time to backdate.