And there is also an option via spook … but reading the disclaimers, I also believe this may make your system unspported (It works fine on my dev instance though) frenck/spook: Spook Not your homie (github.com)
Unfortunately all of this solutions can’t solve my problem. I thought it would be possible to add past values to an existing entity. But Homeassistant has a different opinion I don’t understand why import hasn’t been available as a standard feature for a long time.