Can not a simpler approach give you what you're looking for? capture the 3 which is preceded by 0s, remove those 0s and preserve the 3.. 
my $str = 'hello kitty 003x009 spanish';
$str =~ s/0*(3)/$1/;
print $str;

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In reply to Re: regexp: non-capturing grouping in replacement possible? by biohisham
in thread regexp: non-capturing grouping in replacement possible? by diweooy

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