I would probably write that as:

my $pattern = '...';
$temp =~ s/${pattern}.{6}//s || $temp =~ s/.{6}${pattern}//s;
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Not sure you need the /i, as your example uses numbers.

Instead of creating a whole new variable to match the 321, is there a simpler way to reverse the $pattern variable explicitly in a regex?

But what if the pattern is more complicated? And why do you consider creating a "whole new variable" such a big deal? I guess if your pattern is just a simple string without characters special to the regexp engine, you could write

$temp =~ s/${\scalar reverse $pattern}.{6}//s ||
$temp =~ s/.{6}${\scalar reverse $pattern}//s;
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but I wouldn't. The following is, IMO, much simpler:

my $rpattern = reverse $pattern;
$temp =~ s/$rpattern.{6}//s || $temp =~ s/.{6}$rpattern//s;
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