Add a nested nav table after navigator is loaded - is this possible?

This is a long shot, but I've been lucky before, so here goes...

Have any of you mensches ever figured out a way to generate a nav table after the root nav table has been loaded? Context is that I have a function which (step 4 in the screenshot) which will return a nav table, but it takes a user-entered parameter to run. Once I enter the parameter and 'apply' it simply lists the nav table as a normal table in the preview pane, but what would be wonderful is if it somehow rebuilt the nav tree now that the elements of the nested table exist. I know, I know... I'm stretching here, but you never know! If this is a fool's errand, and someone knows this for a fact, let me know please.