#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

use Tie::File;

tie my @records, 'Tie::File', 'pm_1069470.txt';
s/user={hhhfj}jshdfjhdfjh\\=/user=newvalue/ for @records;
untie @records;

##</code><code>##

$ cat pm_1069470.txt
blah blah blah
user={hhhfj}jshdfjhdfjh\=
whatever
user=something else
user={hhhfj}jshdfjhdfjh\=
other data

$ pm_1069470.pl

$ cat pm_1069470.txt
blah blah blah
user=newvalue
whatever
user=something else
user=newvalue
other data