#!/usr/bin/perl
use strict;

my $str = '(((
\\begin{align}
\\frac{d_l}{2}< |\\epsilon_H(g(m))| <\\frac{d_r}{2} 
\\frac{d_l}{2}< |\\epsilon_H(g(m))| <\\frac{d_r}{2} 
\\end{align}
(((';
my $regex = qr/(?:\\begin{align}|\G(?!\A))(?:(?!\\end{align})[^(])*\K\(/p;
my $subst = '\\\\left(';

my $result = $str =~ s/$regex/$subst/rg;

print "The result of the substitution is' $result\n";