Thinking on it some more, I don't think it's a good idea. You probably can't get the cut end to sit flat in the seat, and given that C/O springs are not as stable as big springs that's a problem.
Spring stability in general matters especially once the axle seats start rotating (this tends to c*ck the spring/make it bow in the middle). Axle rotation happens when you adjust pinion angle and as the suspension moves.
That's separate from the possibility of cutting them so short they fall out with the shocks installed and the rear suspension at full droop.
I'd look at shorter springs in the same rate and maybe consider shimming as a method of fine-tuning ride height.
Norm