Unfortunately no. By fast googling I found this: Protip: How to get shell in actual homeassistant (or addon) container when using Hassio
… which I did not find earlier, shame on my googling.
But at the moment I don’t want to hassle with this, my use was just to get backup and update in one button operation, which would be neat, but not necessary. I want to keep my HassOS as untouched as possible, to maintain easier restore scenarios.