Let me fix data points
If I have made a mistake entering a data point, I'd like to fix it after I entered it (maybe only within a certain time window).
I'm thinking something like interactive rebase in Git:
http://technosorcery.net/blog/2010/02/07/fun-with-the-upcoming-1-7-release-of-git-rebase---interactive---autosquash/
i.e. entering:
21 100 "donation to xyz"
21 25 "fixup! donation to xyz"
would end up as:
21 125 "donation to xyz"

You can do this from the Data tab.
Let us know if you meant that there should be a way to do it via the bot.
Actually, for the common case of Do More goals you can do exactly what you show in your example, since Do More goals are auto-summed.
PS: I think this note goes out as email to everyone who subscribed to this idea. Can someone confirm that you can reply to it and that goes to support@beeminder.com? Thanks!