Do you want to correct default of an element in a CatchChangeDefaults notify handler of this element type.
It was need for me too. I asked about it year ago or so. May be something has changed for 9, but unfortunately the answer was like this:
" it's forbidden to change the default of the element from the notification comes during "CatchChangeDefaults" notify (there is a
safety mechanism against endless loop in the infobox). But you can change the other defaults. "
My goal was to use a change of defaults, namely pen color, to trigger other changes in the defaults. For example, if user sets pen to 164, change current layer to "text" and turn on starting arrowhead.
This seems to work in the settings menus. Only if the change is made in the Info Box is there a problem.
I wondered about a feedback loop, so I created used one of the routines from the API example set to send a text string to the report window every time the defaults are changed, and whether or not the exact function was called. Archicad did not seem to consider a change made by my Add-on to be a change of defaults.