I'm a doctor, not a mechanic
From Unreal Wiki, The Unreal Engine Documentation Site
The Script Editor is where you can make real changes to the gameplay of Unreal, beyond simple level and item creation. You can Create A Subclass or recompile classes that already have actors in the map (but note: Do Not Alter Default Packages!).
- Pasting code from a text editor confuses the syntax highlighter, and the pasted text may appear black on black. Double-click the class name in the list on the left to refresh the highlighting.
- the Default Properties properties block of a class is not displayed in the editor, and adding one will cause an error. Access defaults properties of a class by right-clicking it in the Actor Browser.