What is the current construction? Is there a bearing ridge beam or are there collar ties?? The load is the same adding just few lbs for the knee walls (if I am understanding your question correctly) but if you have a non bearing ridge beam with collar ties, you should not break the collar ties...
I've got a client who wants to build his walls with a 10 degree outward pitch. They are the "non bearing" walls but with 2' overhangs and 128 psf snow load on the roof, I am still concerned with the detail. There is also a 4x10 beam running parallel directly over the wall and the 2x6...