Lock a textarea/textfield for editing

Sure, just don't use a TextArea / TextField ;) The point is the kind of function you're using determines the behaviour of the gui element. The GUIStyle determines the look.

 GUI.Label(yourRect, "The text field text", "textfield");
 //                                             |
 //                                             \__ Style name that should be used.

Same for GUILayout:

 GUILayout.Label("The text field text", "textfield");