I successfully created a form, can display it, enter values, store them, exit the form and read the entered values.
Also I managed to add a 'custom' menu option (besides the standard 'Save') with it's associated callback function.
How can I alter/change a value of a form field from the callback function that is invoked by a form menu callback?

E.g. A form has the text field 'note' and the user should be able to select a predefined string via the form menu, which is selected from a appuifw.popup_menu().

TIA Martin