Fateric + Tankengine
LEM, you know better than this.
I'll tell you why you must set 1013 as soon as cleared to a FL, and QNH as soon as cleared to an altitude: in not doing so, you create a disagreement between two values, the figure set in the altitude selector and your alimeter setting; you open a trap in which you might fall quite easily if "distracted" by something else.
Do you know that the most frequent excuse after mistakes in the sim is "...we were distracted by..."?
So, in other words, if you forget to change you will bust the altitude assigned, and that can be very dangerous.
It is a must to always make the two values agree, academics notwithstanding.
Just make a habit of it, and if ordered to level at an intermediate altitude/level, just apply the same: cleared to a level=1013, cleared to an altitude= QNH.
If requested to say passing level or altitude, use the standby, or even your brain if it's still producing some useful work
LEM