Change 100items at the same time,from "Clear target prior to import" to "Only update imported cells"

Hi there!

I would like to know how can I change one settings characteristic in my Actions. In particular, would be to change from "Clear target prior to import" to "Only update imported cells" in 100 items at the same time, rather than doing so 1 by 1. 

It would be very usefull.

Thank you in advance Community!