In your case, LibreOffice allows you to save the file as Flat XML (e.g., .fodt), and the document will be written as a single uncompressed file. Unfortunately, few apps have a feature like this.
$ ls -hl todo.fodt
-rw-rw-r-- 1 dotancohen dotancohen 150K Apr 7 16:41 todo.fodt
$ ls -hl todo.odt
-rwxrwxr-x 1 dotancohen dotancohen 117K Apr 6 12:01 todo.odt
$ wc -l todo.fodt
1983 todo.fodt
$ cp todo.fodt todo-edit-one-line.fodt
$ libreoffice todo-edit-one-line.fodt
$ diff todo.fodt todo-2.fodt | grep "+ " | wc -l
19