Manual data retention remarks

Here in the manual of data retention is suggested to change the default retention policy to 2h, but does that not mean if you do this on an existing database, data older than these 2 hours will be deleted (immediately)?
If this is so, I would recommend changing the manual by first creating not the default retention policies and then as a last do the default? Or am I misunderstanding something.

Furthermore CQ is putting data in a new measurement, I rather keep data in the same measurement. I think it will be a lot of work rewriting eg. grafana panels to use a different measurement because a user wants older data. Not really a good solution for a devops like situation.

Please re-write if these assumptions are correct.

Just reading this year old post, is anything happening with this?

If you store the new down-sampled data in the same measurement, and the data retention policy on that measurement is, say, 2 hours, your newly stored downsampled data will be expunged after 2 hours. Data retention policies are on a database level – a data bucket if you will – not on a measurement or field level.

Storing your data back to a measurement with a short data retention policy would have no effect on the retention of that data.