Let's not forget that pack/unpack are another good way to do this sort of string mangling:

#!/usr/bin/perl

$target = "blah0x4445434C41524520405420blah blah";

$target =~ s/0x(([0-9a-f][0-9a-f])+)/pack('H*', $1)/ie;

print $target, "\n";
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