my $newfile = "svs.conf.$$";

open my $in, '<',  'svs.conf' or die "Can't read svs.conf: $!";
open my $out, '>', $newfile   or die "Can't write '$newfile': $!";

while (<$in>) {
    s/\bbe_address\b =/, $new_value;
    print {$out} $_;
}

close $out;

rename( 'svs.conf', $newfile );