If you want to change the submitted value and also alter values in other posts based on what is submitted you would need to create an acf/save_post function.
In this function you would need to
- Get all the posts
- Check the value of the field in each post
- Alter the values (or not) in all of the posts based on the value submitted by for the current post
For more information on acf/save_post http://www.advancedcustomfields.com/resources/acfsave_post/
