Please note that the following answer only applies to clients residing in Germany.

Switching from a joint tax exemption to a single tax exemption mid-year is not possible. You can set your joint exemption to expire at the end of the calendar year. After your joint tax exemption expires at the end of the year, you can then set up a single tax exemption in the new year or set up a new joint tax allowance with a different spouse. If your joint tax exemption is currently configured without an end date, please change the exemption to expire at the end of the current calendar year. Thereafter, no further action is required on your part until the year's conclusion.