replacing widgets in packing boxes

[Dirk Koopman <djk tobit co uk>]

I have some container or other, say a packing vbox, in the middle of a
huge screen and I have done $vbox->pack_start($widget, 0, 1, 5);

I now want, without rebuilding the whole screen from scratch, to replace
$widget with another, possibly completely different, $newwidget.

Is this possible?

I have the reference "$widget" available to me as well as its parent's.

Dirk