What would be the problem with that? I think it would even be a benefit, if the container could signal everybody if the public IP changes. The BitTorrent client transmission - as an example - needs to be restarted if the VPN exit address changes, otherwise it won’t get any connections anymore.
Anyway… if one starts the hummingbird container with -e "EXTRA_ARGS=—persist-tun“ then the hummingbird client can be made to reconnect by sending a USR2 signal to the process. Thus a command like
docker exec -it hummingbird /bin/sh -c 'ps -A | sed -nE "s|^\s*([0-9]+)\s.*/usr/bin/hummingbird.*$|kill -USR2 \1|p” | /bin/sh'
would initiate a reconnect.