It would be nice to have some sort of visual indication that an item has properties changed in the properties panel.
An example of when this would be useful is adjusting slurs. Manually adjusted slurs would display in a different colour, so I can tell at a glance which slurs are default and which I have adjusted by hand.
My instinct for this feature is to draw the item in a different colour, similar to the note colour options for different voices and range. This would allow the colouring to be turned on and off as needed.