I'm not sure about any clear guidance (lots of documents with varying things in), but regarding the semicircular rule, it is in force and note that it *does* apply below the TA.
As you say for VFR it is only recommended, however it is mandatory for IFR - you should fly odd thousands of feet for magnetic track 0-179, and even thousands for magnetic track 180-359. The only exception to this is if flying "in accordance with instructions from the appropriate ATC unit or in accordance with holding procedures notified for an aerodrome" - there is no explanation for what you're supposed to do if there isn't a suitable level available, e.g. in the situation you need to remain below some CAS but above MSA...