If you say if you want to change the nature of trust (from negative to neutral or positive) it simply means that your old feedback is not valid.
Better to delete the feedback and write the new one.
It just looks weird though if it's a really old trust rating.
Or maybe an edit button wherein the feedback will turn to neutral, negative or positive or vice versa. Maybe more feature that even the description will be edited as well for some adjustment or add another description but doesn't touch the date it has been given or show edit history just like what we see on self-moderated threads.
Maybe positive to neutral or negative to neutral would be a good idea. I don't think negative to positive or the other way round is really practical. Also editing might be interesting in appending to stuff after an [edited on: date] if you forgot something or maybe an edit within 30 minutes much like posting for if you make a mistake but don't want to start over.