I am updating my gearing for a cross-country tour, and I am thinking of tinkering with my cassette to make it more hill-friendly. I have a trek 520 with an 11-30 8 speed hg-50 cassette with a 26-36-46 crank. I want to remove the 11 tooth sprocket and add a 34 tooth sprocket on the upper end of the cassette, making it 13-34 climbing machine. Is this a doable operation or do I need to get a new cassette. Thanks for any suggestions.