Why is this something that is NOT about SQL?
The creation of the error log files is something that is built into the application. So there not much chance of you making a change so that it only has one file. You could probably do some sort of file joining via a batch command or VBScript, but you would have to do that every time the SQL service was restarted.
What's the problem with having more than one file anyway?
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Colt 45 - the original point and click interface