The new alternate vendor feature is a welcome addition. However, there is no way to bulk remove an alternate vendor. Additionally, when you assign a new Preferred Vendor, the previous preferred vendor is automatically moved to an alternate vendor. This should be a prompted operation, not one that happens by default.
A perfect example would be Herman Pro AV, which was acquired by ADI. I changed the Preferred Vendor to ADI and now Herman Pro AV is an Alternate Vendor. Now I have to go through each part 1 by 1 to remove the alternate vendor.