Can I achieve more than one of the same peak from the same workout? (e.g., 1st and 2nd highest 1-minute power for 2017 from the same workout)
TrainingPeaks only looks for the single highest peak at a given duration in a workout. So if you do your first interval workout of the year and set your 3 highest peak 1-minute power performances for that year so far, only the highest will be recognized.
How can I remove Peak Performances from my list?
If you long press a peak on the Android app or swipe a peak on the iOS app from historic Peak list you can remove it. You may want to do this if you have erroneous data from that workout or if you live at altitude but only race at sea level occasionally. Removing a Peak Performance will not alter the original workout or data in any way, you may still want to go to the original workout to correct bad data.
Will my previous workouts update as I set new Peak Performances?
No. The Peak Performances listed in the workout summary will stay the same as the day the workout was uploaded unless you recalculate the workout. This will give you a snapshot in time of what those Peaks were on that day. (i.e., if you set a 3rd best peak for the year in January, but by the end of the year it is only your 8th highest, it will show as 8th in the Peaks tab for that year, but when you go back to view that workout it will still show 3rd).