I don't know why the overriding is not working if you add a dialog with the same name to your mod.
To override it via story, undefine the database for the regular default dialog (
NOT DB_Dialogs(S_TUT_Humans_Female_Magister_Priest_000_9d17cf06-6fad-49a8-82de-54518a9bf5df,"TUT_LowerDeck_Humans_Female_Magister_Priest_000");) and then define a DB_Dialogs entry that links your dialog to her. You can do this in the INIT section of your story goal, but you have to ensure that your goal
initialises after the story goal that assigns her default dialog (TUT_SourceCollars) has been initialised. This means:
* your goal must only initialise after the
RegionStarted("TUT_Tutorial_A") event (the parent goal of TUT_SourceCollars, Tutorial_PrisonShip, completes on that event and hence its children initialise after that event)
* you goal's name must come after the string "TUT_SourceCollars" when alphabetically sorted (goals are initialised in alphabetical order)