If you are instructed to descend FL80 without a B restriction, then it can be disregarded, but if you have been told previously to descend FL100 level B and then recleared by another controller FL80, you must comply with B. However being routed direct beyond points A/B cancels the restriction unless reinforced.
ALL levels published in the STAR charts have the proviso "or as instructed by ATC", if there is any doubt,
make sure you check with ATC or a serious consequence may soon happen.
On a similar note of STARs, speed control is the same. Those published can be ammended by ATC, so if instructed fly IAS 300kts+
until advised then don't ever slow to 250kts just because the STAR says so. You'll be suprised just how many still do, and their suprise when the subsequent paperwork arrives in the office 3 days later.
