Hello,
Each component has its own callback, and only thing that you need to do to change it is to rename it, everything related to its name will be changed automatically.
If you want to delete the callback, find it in Code Browser section (top left) and under Callbacks, delete it. I don't think it's possible to have multiple callbacks so you'll have to embed your code into one.
Answer edit:
Click the component, on the right-hand side in a Component browser, in the section Callbacks, just below the list of components, there's ValueChangedFcn dropdown menu where you can select/remove or create another callback.
