I don't think the language in §20.5 is establishing a "separate set of rules." It's something totally unique that only applies to the trial manuscript and not something that must always be done. The manuscript is a test and quite often instructions in many other institutions have rules for testing that are different than in "the real world."
The NLS course is only a gateway to the world of braille transcribing and follows the Rules of UEB and Braille Formats and provides consistent cross-references to those codes for students' further study. If you are at all familiar with the course, you would know that the division of hyphenated compound words is mentioned in Lesson 12, on page 12-10.
In the instructions that precede the Lesson 12 exercise, students are given this further instruction:
"... When room permits, hyphenated-compound words may be divided between lines, but only following the hyphen. ... "
So again, —the §20.5 instruction is only a temporary request between the grader and the student. It is not a separate rule.