Just unpack it into a differently named directory and copy the savegames from your current copy of the game (hint: those would be the most recently modified files in the game directory).
I can look into preparing a fix of some sort, but to do that I'd have to have a copy of the borked-up version of the game so I can find out which files differ.
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"God. Can't you people see I'm trying to commit a crime against science and nature here?"
-- Reed Richards
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