I agree with Pete, the construction of the spring prevents it from working upside down. try it if you wish, but its several hours spent underneath a car for no effect!!
From what I can see, removing no. 12 and placing it under 15 would lower the suspension, but would also soften it. I would suggest splicing 2 springs. Move the eyelet leaf (no.15) closer to the top, but add a leaf giving 6 leaves which would stiffen the front suspension rather than soften it.
Other than this you have the option of paying someone to reverse the eyelet of no.15, removing the plastic liners, sitting the spring on the floor, with a mate standing on top and heating it wiath a set of burning gear until the arc of the spring softens. lower suspension, but not stiffenend.