When editing a conpherence room, there is no way to undo this. Since images cannot be deleted, there is not even a manual way to do it for every change.
I can't really figure out what happened in Phabricator that you would need such a feature, or only need it in Conpherence. We don't have undo elements as a common pattern (its in diff comments only).
Filing feature requests without problems and just a solution makes upstream support very time consuming. We don't want to spend time debating why a feature solution isn't a good fit, and would prefer just to find a solution to your problem. If our "describe problems" documentation isn't clear, what can we do to make it more clear?
Problem: The settings of a Conpherence room were changed mistakenly. I need to undo the change. Resetting Conpherence room images (part of the accidental change) to the default is not possible.
P.S: Since you use transactions everywhere, I assumed they would make the implementation of an undo action rather simple.
If it's not as simple, at least resetting the icon to the default would be helpful. Project pictures have such a feature.
As a temporary workaround, I can upload a new image.
something like T8972
T8972 is the only reason this task was opened.
(or simply a mistake) occurred.
This is hypothetical. We don't take feature requests around hypothetical scenarios. Please (again) read our documentation on feature requests: https://secure.phabricator.com/book/phabcontrib/article/feature_requests/#hypotheticals