If the field  has a connected basic data window. The List can be extended by adding lines in that window, mostly  basic data.

Example Sales Charge Groups in Sales Basic Data

or Purchase Charge Groups in Purchase Basic Data

That is helpful, I am still searching for where to add a group but that make sense

In Enterprise Explorer you can use the zoom in (F9) to open the window (if existing) that contains the basic data of the field.

In Aurena enabling field description, the description shows the path were data can be changed.

Thank you