Removing Teacher Recommendations?

I am applying to a handful of schools via the CommonApp, and I assigned two teachers to all of my schools in September. This month I asked another teacher to write me a LOR, but many of the schools only allow two teachers to recommend. I don’t want to offend a teacher by removing them from a couple schools. My question is: are teachers notified if you unassign them?
P.S Neither of the original teachers have completed their letter, so I have the option to unassign still.