To have the label arrow draw itself using the settings, uncheck the 'use symbol arrow' box. This seems backwards to me.
ASSOCLP_PARVALUE can only be used with associated labels.
Associated labels must be set up in the default settings before the element is placed. When the label box is checked for placed elements, those new labels will take the object and settings of the default for the tool. If you're going to turn a bunch of labels on, set the default up first.
Editing associated labels: The 'Label Settings' button is always greyed out in selection settings. To edit the label, you must select it and do Cmd+T.
Editing and saving label object while a section window is open: when you rebuild, Archicad hangs with 100% CPU.
Drawing your own arrowhead is difficult bordering on impossible. The scripted symbol is intended as data/icon only. Let the subtype draw the arrow, or turn it off with the checkbox.
Why does the 'label elements' checkbox sometimes fail after saving a label object? You can't label an object on other than its home story.