No, each customer can have only one effective tariff for the given calendar year. This constraint is due to ambiguity of commission calculation in cases when same month salary is processed at various times when different tariff plans are effective. Therefore, tariff changes are possible at the end of each year, when subscription is renewed. Selection of the different tariff for the next year can be done anytime during the current year in your customer area under "Settings" / "Subscription".
We recommend our customers to set the settings for a tariff change before December 15 of the current year. In exceptional cases when new customers have just signed up for our services and have no bills (salary) processed in the effective year, tariff corrections are possible by contacting our support department at firstname.lastname@example.org.