I actually managed to solve this problem, the goal was to dynamically display a random hierarchy child as root parent in the displayed hierarchy table. Without having to reload from source data.
(See explanation above)
An expression dynamically determines which Node# field from the source table to display for each column and for each row in the output pivot table. Im using the pick() function for this, as it turned out dollar sign expansion is not re-evaluated for each dimension value.
As I think this is quite an interesting case, I attached the solution to this post for future reference.
This example shows how to dynamically rearrange hierarchy tables, displaying a user-defined child node as the new hierarchy root parent, without having to reload from source.
There's just one problem left, in order to make Qlikview recalculate the dimension values after changing to a new root node, you need to manually collapse and expand the dimensions in the pivot table.
Does anybody know if it's possible to have qlikview calculate this automatically using the OnChange and OnInput triggers on the inputbox?