Allow a designated tag to overwrite another tag. Suppose you've tagged Task A from 10:00 to 10:15. Then you look and you see that you took a phone call - Task B - from 10:05 to 10:10. If you just tag Task B from 10:05 to 10:10, you'll have that portion double-tagged. But I'd like to manually overwrite so that Task A is broken into two segments (10:00 to 10:05 and 10:10 to 10:15, totaling 10 mins) and Task B overwrites the time for 10:05 to 10:10, totaling 5 minutes.
Actually there is a way to do that now. Not necessarily the most straightforward (usually you can tag many different ways, this only works this one way)
If you're on the applications timeline (I assume would work on Docs timeiline but I've only tried on Apps) then the bottom half of your window is a list of all the apps and their times (with the checkboxes).
Select the time you want to tag-replace, right click it and from the tag menu select a tag from the recents list or select 'add a tag' and choose one. This replaces any tag(s) with the one you selected.
Beware, I said replaces *tags*. If it was multi-tagged on purpose all will be replaced with this one.