Regarding the undoing of deleting a callback, it is undoable. You can either use keyboard shortcut ctrl+z (Be sure to click on the component browser to give the window focus, there was a bug using the context menu that focus got lost). Or you could switch to design view and use the buttons in the toolbar.
When you are in code view, those buttons control undo and redo actions in the editor. When you are in design view the buttons handle all actions outside the editor. The keyboard shortcuts work based on what has focus.
Regarding callback reordering, we are aware this is a painful limitation and are working on improving the experience.
Regarding the turning off the code analyzer, this is not currently possible in App Designer. The "enable app coding alerts" is a separate feature specific to addition alerts App Designer displays to help with Obeject Oriented coding and some graphics limitations. It does not control the code analyzer. I've added a request to add control for code analyzer.
Thanks for the feedback! Melissa