#!/usr/bin/perl

use strict;
use warnings;

use XML::Simple;

my $in_file = "in.xml";
my $xml_file = 'out.xml';

my $xml = XMLin(
    $in_file,
    KeepRoot => 1,
    ForceArray => 1,
);

# added ->{content}, so now attributes are preserved and stay
$xml->{importrecord}->[0]->{aktionen}->[0]->{transaktion}->[0]->{aktion}->[0]->{parameter}->[0]->{attribut}->[0]->{content} = 'Anlegen';

XMLout(
    $xml,
    KeepRoot => 1,
    NoAttr => 0,
    OutputFile => $xml_file,
);