You can use the User Input field to specify any kind of text. The text will be appended without any change to the end of the ADF input. This way, you may access some keys that are not (yet) available in ADFinput. For example, you can use it to specify the OCCUPATIONS key once you know the symmetries of the orbitals.
Note that at this point in time you can only add text to the ADF input file, not to the input of any of the property programs.