In article , wrote:
I don't think I would "bob up and down" on a cruise clearance. I
would request a block altitude assignment if I want to "bob up and
down."

A cruise clearance *is* a block altitude assignment.

A cruise clearance is also an instrument approach clearance, so once
I leave the last assigned for all I know the controller may be using
my Mode C as a de facto report out of that altitude.

You own the altitude until you report leaving it. Your mode C does not
count as reporting leaving the altitude.