It's just a tie.

use strict;
use Tie::File;

# skipping all sorts of fun to get to this:

tie @array, 'Tie::File', "$mf_dir$filename", recsep => '}', autochomp 
+=> 0;

$array[$user_section] =~ s/username =\> $username/username =\> $newuse
+rname/;

# or something like that
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