The metric system has broken with its own past, though. The breaks were true breaks, not just elaborations, but they were executed with great care for compatibility. 1m has been defined in four or five different ways, depending on how you count.

There's a lesson here: There is a middle ground between preserving legacy and causing problems by deprecation.

So what are the “problems by deprecation” you see in the current context of redefining Pluto as not a planet? Having to reprint interplanetary tourism guides?

It's just another minor thing to complain about for the people who like to complain about science.

Nothing minor is major. Some of them are minor and worthwhile, some are minor and not.