Use a Docker image with an editor and connect the volume container:
docker run -v $OVPN_DATA:/etc/openvpn --rm -it kylemanna/openvpn vi /etc/openvpn/openvpn.conf
The run-time image (kylemanna/openvpn) is intended to be an ephemeral image. Nothing should be saved in it so that it can be re-downloaded and re-run when updates are pushed (i.e. newer version of OpenVPN or even Debian). The data container contains all this data and is attached at run time providing a safe home.
If it was all in one container, an upgrade would require a few steps to extract all the data, perform some upgrade import, and re-run. This technique is also prone to people losing their EasyRSA PKI when they forget where it was. With everything in the data container upgrading is as simple as re-running docker pull kylemanna/openvpn and then docker run ... kylemanna/openvpn.
Split tunnels are configurations where only some of the traffic from a client goes to the VPN, with the remainder routed through the normal non-VPN interfaces. You'll want to disable a default route (-d) when you generate the configuration, but still use NAT (-N) to keep network address translation enabled.
ovpn_genconfig -N -d ...
You can pass multiple (-e) options to ovpn_genconfig. For example, if you need to add 'duplicate-cn' and 'topology subnet' to the server configuration you could do something like this:
ovpn_genconfig -e 'duplicate-cn' -e 'topology subnet' -u udp://VPN.SERVERNAME.COM