That's kinda true... alginate shrinks as it dries out and can be used make small reductions (nothing like 25%). I have seen it used to good effect in stage scenery. However at the size and level of detail we're talking about... not so useful. Repeated use of black rubber moulds can shrink a model (the oft-cited proof of a recast) but it takes 4 or 5 successive bakings to significantly change the size of a model and at current prices that's about £300... you'd have to really want to shrink that model! Plus you get distortion you can't control as a model shrinks, so thin pieces will shrink more than thick pieces causing warping, loss of detail and overly-brittle elements. I don't know any magic substance that expands as it sets, thereby enlarging the model... I wish it did exist sometimes!