An existing window in the model should inherit certain properties when updated or modified such has casing option, colors, size.
For example you have a model with certain kind of windows but you want to change for another type you select them, pick another type and you have to re-edit everything : color of frame, of casing, dimension, size of windows, color of line .... This could just be taken as DEFAULT from EXISTING object. NOT object from library.
So fare this is the biggest waste of time when projecting with archicad.