Unlisting a rule won’t work. The problem is going to be that, when you have Inform set up to understand a command that applies to multiple objects, it figures out what each of those objects are and then applies the command to them one by one. For instance, “take all” gives you a separate “taken” for each object.
So if you want a single response to “obliterate all,” you might have to write a rule that catches that the player is obliterating multiple objects, runs once, and then doesn’t run again the rest of the turn. Check out the example “The Left Hand of Autumn” in the documentation.
If you just want to print a clever response to “obliterate all” and don’t much care about which particular collection of things is being obliterated, you can try this:
To decide what action-name is the action-to-be: (- action_to_be -).
Rule for printing a parser error when the latest parser error is the can't use multiple objects error and the action-to-be is the attacking action: say "One at a time!"
Note that it will give the same response to “attack jordan and taylor” as to “obliterate everything”.