You always can change the extension of a file. But this doesn't mean that
the content of your file is being changed.
What you should do is import the file. (If it is a "fixed-width" or
"delimited" textfile it is possible in access. After that you should export
the imported table to the format you like.
Everything depends on the situation.
This article http://support.microsoft.com/?id=304206 shows how to use
non-standard extensions. It's about importing rather than linking, but
the same principles apply.
