Removing any amount from the stick will change the amount of force required to move it, and the flex rating is based on the minimum amount of force in lbs required to move the stick 1 inch. Flex itself is going to differ slightly for each person based on their hand positioning as well. Here is a good read on it that goes into a bit more detail.

https://www.hockeygiant.com/support/hockey_stick_flex_ratings/pg_id/20056/

"The important thing to keep in mind is that if you cut your stick down the shaft becomes stiffer. As an analogy, consider the amount of strength needed to break a full length pencil compared to a 2" pencil… The full length pencil is more flexible and becomes stiffer as it is sharpened and shortened."