The only reason I can imagine for using substitution in a situation like this is if the block of text to be changed is a sub-block within a larger text block: 

c:\@Work\Perl\monks>perl -wMstrict -le
"my $str = qq{cat\nman\ncat\ndog\neel\nman\nman\ncat\ncat\nman\n};
 ;;
 my $sub_str = qq{cat\nman\n};
 my $n = 3;
 ;;
 $str =~ s{ (\Q$sub_str\E) }{ join '', map qq{$_ $1}, 1 .. $n }xmsge;
 print qq{>$str<};
"
>1 cat
man
2 cat
man
3 cat
man
cat
dog
eel
man
man
cat
1 cat
man
2 cat
man
3 cat
man
<

[download]
(The \Q...\E metaquoting (update: of the interpolated $sub_str string) is necessary so that newlines are matched literally when the /x modifier is used.)

Of course, once you have this structure, it's easy to go to full regex search/replace: 

c:\@Work\Perl\monks>perl -wMstrict -le
"my $str = qq{cat\nman\ncat\ndog\neel\nman\nman\ncat\ncat\nwoman\n};
 ;;
 my $sub_str = qr{ cat \n (?: wo)? man \n }xms;
 my $n = 3;
 ;;
 $str =~ s{ ($sub_str) }{ join '', map qq{$_ $1}, 1 .. $n }xmsge;
 print qq{>$str<};
"
>1 cat
man
2 cat
man
3 cat
man
cat
dog
eel
man
man
cat
1 cat
woman
2 cat
woman
3 cat
woman
<

[download]
(Update: Note that metaquoting is not needed here because $sub_str is a Regexp object: \n matches a literal newline.)

Give a man a fish:  <%-{-{-{-<

In reply to Re: Can I get some help with a regex please by AnomalousMonk
in thread Can I get some help with a regex please by misterperl

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