I can't think of a way to bulk change Feedback questions for existing Feedbacks.

When you change a Feedback template and have a Feedback based on the template there is only an option to add or delete questions from the template. This means that you will need to edit each Feedback individually.

There is a way to set up a Feedback so it is used in other courses by adding the Feedback to the Front page and Mapping the Feedback to courses.  When the feedback question is edited it is changed in all mapped courses. You have already got separate Feedback activities in your course so there isn't a way to combine these into one Feedback activity the mapping needs to be setup at the beginning.

Regards