I used the simple expedience of using a cut off wheel to trim 13 CM off the bottom end of the coils. I did some measurements with the wheel free from any springs, and confirmed to my satisfaction that there was plenty more drop available before things started bashing into one another. If I were to do it over, I would probably only cut 7 cm off, so it would fit more cleanly on the lower spring perch, but only do this after they are well and truly broken in. Wouldn't want them to settle unevenly. I will say that a lot of people would be shocked and upset at the notion of cutting springs, but done very conservatively its not a huge deal. There was no noticeable change in ride quality, and the change in handling was predictable as a result of changing the rake of the car.
I've done this on a few classic cars, cut the springs for a drop in ride height.
I had a 71 Ranchero GT I wanted lowered, bought some 1.5" lowering springs for a 71-73 Mustang (per an old Ford interchange book I had) and they were WAY too soft. In short I actually cut the stock GT springs which were much stiffer to give me my drop.
Like you said though need to let the settle, I actually cut those springs down twice, first time only came out about 3/4" lower then settled to 1" after about a month of driving. After another month no change I cut them again and all said and done ended up with a 1.75" drop over stock.
I wouldn't do that with today's cars, but certainly do not see the any harm in trimming an aftermarket set down to fine tune your preferred ride height.
2013 V6 Performance Pack - Stock..... for now