Although this is not an advisable way to navigate in your channel (doesn't follow the design guidelines), it is possible in the SDK to do this....
In your event loop, you could make to of the posters select between two different categories (that you initialize from the xml feeds above), and change the filter bar based on the selection. Remember to call Show() after changing the filter bar to make the screen refresh.
else if msg.isListItemSelected() then
if (msg.GetIndex() = 1) then
screen.SetListNames(Categories2)
screen.Show()
else if (msg.GetIndex() = 2)
screen.SetListNames(Categories1)
screen.Show()
else
newIndex = showSpringboardScreenWithNav(Items, msg.GetIndex())
screen.SetFocusedListItem(newIndex)
endif
endif