The WALL_ID global is only filled by ARCHICAD in DW object, and “classic” labels, so building a function in accessory elements connected to that might be problematic.
The current fix named optional parameters in the accessory elements for walls contain geometric information about the selected wall’s shape and end cut angles (ac_angles, ac_top_poly, ac_bottom poly etc.,), so it’s possible to calculate special points of the wall using trigonometry, most of the cases. You can display this info in 2D, but the ID-relation is still not solved.
To tell the truth, the Accessories may be unreliable in lots of geometric cases, and haven’t been updated for many versions now.
If you have not found this wall global list yet, please, check, maybe all needed geometric data is available in normal labeling function as well.