How can I import/rewrite settings/content types/blocks/etc from live with the newly developed features on dev?
IMHO, using git for that works quite well.

You have a production branch and a development branch (and possibly many feature branches). Locally, you are on the develop branch, you make your changes there, export and commit your changes there

Before you do a deployment, you switch to production branch, do a config export ,sync it down, commit it, merge develop into production, do a local config import to make sure that things are consistent and then deploy.

A useful presentation for this is https://de.slideshare.net/nuvoleweb/advanced-configuration-management-with-config-split-et-al, for example slide 39, although that focuses more on working with multiple developers, but the process with production is similar.