Think you hit the nail on the head - from what I can see it will be a case of altering/moving
every item in that layer (bummer). I also think the box/background sprite is of a particular size and I can't simply alter it in this code (???) and therefore make it larger and also make the contents larger to suit. But at least we know a bit more now, plenty more to work with

You can move the entire layer -- coordinates of objects are relative to the layer, not necessarily the screen itself.
So try doing something like
...
/layer>
Although if you want it positioned higher you'll need to use negative coordinates for y.
Give the layer dimensions as well (w and h) equal to the size of the black box. and reposition all elements once relative to the top left corner of the box itself (so, box would be x=0, y=0 etc.). Then you can easily move the layer around and x/y will be the same as the black box.
If you want to blow the box itself up, you'll need to paint a new one (or look through bitmaps in DATA.ZIP... there might be something there). I don't think you can zoom bitmaps and even if you did, it wouldn't look too good...