always wanted to try that! but people keep telling me it's no good idea!
no seriously:
the FMS contains the correct front course for the ILS **BUT** there's no protection from selecting a wrong one on the course windows.
IF you've tuned the wrong ILS-freq the FMS will give you "RWY TUNE DISAGREE" (or if the freq was changed an the data base was not updated
)
IF the two course selectors DIFFER the course will be crossed out yellow on both PFD's. but still there's no "correct course"-protection, merely a difference-thing.