Another idea is that you update the segment rules to reflect the data you are going to import.
For example, if you have a Product Family of A an B, and product C just came out, update the segement rules so C is no included in the segmentation mix. When you import the data, the rules should take over and place the lead in the proper segment.
I'm not sure if this solves your need but it does provide another way of thinking about the problem