If they don't then what you could do is create a simple script that just adds that line, and Excel will open the files without you having to hassle with making sure Excel interprets them correctly. Of course that's a bit more challenging if they use different separators, but you might be able to find an easy adaptation for your usecase like making a decision about which delimiter to declare based on the filename. Or you could try to analyze the header row to figure out which delimiter to use based on that.