When you copy-paste blocks from a file to another, there is a chance you get the “Block name conflict” warning.
The only option is to move forward with the copying, with various options as to how to deal with the conflicts.
But what if you simply want to abort and fix the names in your own sweet way ? Well, you just can’t.
You might as well hope you’ve saved the file recently and reboot the computer.
So how about adding a “Cancel” button ?