Adding a 45 degree bevel cut to a 90 degree crosscut sled.
Raising this issue again because I was considering doing the same thing - adding a 45 degree bevel cut to my current 90 degree sled.
I don't think you will lose the zero clearance as the only places the blade slots (or kerfs) will meet is on the bottom side of the sled where the blade contacts the sled at the first point. On the top side of the sled, and on the fence, the kerfs will be separated by a small distance and amount of uncut material. Specifically they should be separated by a distance equal to the width of the material of your sled minus the blade kerf. For instance, if your sled base is built out of 3/4 inch ply or MDF, and you are using a full kerf 1/8 in blade, the 45 degree slot should be 3/4'' - 1/8'' = 5/8'' away from the 90 degree slot.
Am I missing something?