1. Is it actually okay to skip practice?
2. Is it actually okay to sabotage yourself to Final B and out for shorter time spent?

Info: The race structure is like these: Brief: Qualifying -> Race Full: Practice -> Qualifying -> Heats -> Final B (only if bad placing) -> Final A (longer than Final B )

The rules wording in Full is exactly the same with Brief, except for "using brief/full". And that rule would mean "don't skip any session" in Brief.