All issues stem from the same cause; namely, the change you made in the for loop needs to be also done for your File0. Change:

write_xml_content($key_file, $source_file_for{$key_file}, $out_fh, ' '
+ x 4);
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to

open my $in_fh, '<', $source_file_for{$key_file};
write_xml_content($key_file, $in_fh, $out_fh, ' ' x 4);
close $in_fh;
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