Pipelines config

I am new with jenkins. I was wondering why if I have a jenkins file with parameters and various stages, and scripts, I can click configure in the webUI, and change the parameters?

Why only the parameters?
What happens if they become incompatible with the scripts? (I can change the parameter types)
What happens if I save the config?
Why is the rest of the jenkinsfile not editable in the UI with no warning a lot of the logic is not present on screen?