I dont see how cutting the spring would weaken it as a whole. Also i don't see any reason why cutting non progressive springs evenly would have any negative effects.
In my experience for example, i recently lowered my car properly with bat struts (not st200's) and roush springs. Like every other car with roush springs my car sits too high in the front. This last weekend i spoke with an engineer at ford and he actually suggested i carefully cut my non progressive front springs. So far I havent seen any reasons which would dissuade me from doing so
