I'd say, "Changed".
Why 'downgrade' Pluto?
'Cause OTHER things in our 'system' are as big, or bigger, and they didn't want to ADD 'planets'!
(Can you imagine the uproar?)
"Only GOD can create a PLANET!!!"
Everything is *updated*. That way they never have to say they were wrong; it's just *a better fit with what we now know*. Science, constantly correcting itself to correct all the errors in the past.