I understand that
/home/homeassistant/homeassistant-update.sh allows me to update to the latest version, and I can see that this script is actually
exec sudo -u homeassistant dash -c '. /home/homeassistant/pyenv-activate.sh; exec pip3 install --no-cache-dir -U homeassistant'.
I was wondering if there was an obvious edit I could make to this to install a previous version of HA (to help trouble-shoot a bug).