I have a Ultegra CS6700 9 speed rear deraileur that came on my bike. Originally the gearing was 12-25, which I changed to 12-27. I was wanting to know of that deraileur would work without a problem switching to a HG50 cassette. The reason for doing so is because it offers a 9 speed 11-32 gearing. I was wanting to get the bigger granny gear so I could more easily go up big hills. Would this new cassette work with just swapping the cassette and adjusting the deraileur to accomodate the bigger gear (also changing the chain to have more length) with the older Ultegra deraileur or would it not shift because of the differences?
The published max large cog for both RD-6700-SS and RD-6700-GS is 30. They can sometimes work acceptably with 32, but they're not designed to and it's hit or miss. The variance is because dropout design is not universal. Putting in a longer b-tension screw or running it in reverse can help. You can also get something like a Wolftooth Roadlink.
Total capacity is 34t for SS and 40t for GS.