It all depends it the response is still in the topics list or not. I know no way to force the geck to use an existing file. He commands, we obey.
As long as you only edit the prompt, the result script, topic, choices or the variables to get the answer you don't need to rename the file, but as soon as you need to open the "edit response" and make any change you have to duplicate the file and rename it.
I don't see what line you mean so you'll have to check yourself. In the VEnding quest, under VEndingCass I found a comment about alice and gloria's death. If it is the one you want, good news, otherwise you have to add it back as a new dialogue in the old fashioned way.