While many utilities provide file naming automation, they're mostly overkill for those cases when you need to make small variations in file content while ensuring the documents group together in a "by name" list.
In the Save As dialog, the default name is the current document name. You can quickly change this to match any existing file.
1. Make the list of files the active element.
2. Click on a grayed-out filename, which momentarily turns black.
3. The Save As field now contains the filename you just clicked.
You can modify the name (adding, say, "version 3") or overwrite that existing file you clicked.
From Jesse the K