PROBLEM: The user has edited the new section without first making the clips unique, so now the old section is edited as well. Undoing these changes is frequently complicated and sometimes impossible without manual recreation or reverting to backups.
PROPOSED SOLUTION: Give all clips that are unique in the playlist a graphical indication of some sort. Perhaps highlight them, give them a colored border, bold or italicize the title, put some kind of symbol or asterisk next to the title -- any number of options would work here.
RESULT: The user will know that if they edit a clip which does not have this indication, they are making a change which affects multiple clips. They will rapidly develop the association that unique edits occur on clips with the "unique clip" graphical indication, and will therefore know instinctually not to make changes which should be unique without first seeing that indicator.
COMPETITIVE INTELLIGENCE: Cubase has a similar feature, but in reverse. Their equivalent of clips are unique by default, but can be explicitly made shared -- in such a case, shared clips receive a special "=" indicator in the upper right corner (see image below). Since FLS uses "shared" clips by default, which are instead explicitly made unique, it stands to reason that it makes more sense for FLS to give a special indicator to clips which are unique.
DEMAND: The lack of this indicator is a common source of frustration on youtube streams, and I have personally witnessed SeamlessR accidentally edit non-unique clips in almost all of his Sonic Academy tutorials. Nucleon vouched for the value of this feature 6 years ago, and there are plenty of other threads complaining about this problem (here's an example).
COST: As quite nearly any sort of indicator will suffice, the implementation cost can be very low. However this must be done in such a way as to not impact the rendering performance of the playlist. One possible approach would be to define a counter variable for all patterns, automation clips, and audio clips, which increments/decrements as instances of that pattern/clip are added/removed from the playlist. In the event that the counter is 1, the playlist clip would then render with the special "unique clip" indicator -- in all other cases, it would render normally.
Example image from Cubase below:
