A regex will do it, if you're careful: 
$old .= (length($old) % 2) ?  'F' : '';

$old =~ s/\G(\w)(\w)/$2$1/g;

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Note that \w includes letters, digits, and the underscore character. If the latter isn't acceptable, use a character class.

In reply to Re: Rearranging a string by chromatic
in thread Rearranging a string by muppetBoy

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