I need a new electrical panel. One electrical contractor looked at the
existing feed and said that he could pull 150A wiring through the
existing pipe and change the main breaker in the 200A panel to 150A so
that the breaker matched the wiring coming in.

Another contractor insists that this is not legal because someone could
change that 150A main breaker to 200A in the future because the panel is
rated for 200A.

My next door neighbor did this and it passed inspection. But was it a
clueless inspector or is it really legal?