renaming with batch file, no overtype?

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I'm trying to script a batch file that renames a group of files. I'm using
this setup currently:

@ECHO OFF
set string="string of text"
rename *.file %string%*.file

But what it does (and what I don't want it to do) is overtypes on the
current filename. Example:

input filename: this is a filename.file
output filename: string of textname.file