Half off-topic, sorry: if you have some spare time on the weekend, you might want to take a look at nftables. AFAIK iptables is also just using nftables under the hood, so you are basically using a deprecated technology.

nftables is so much nicer to work with. In the end I have my custom rules (which are much saner to define than in iptables) in /etc/nftables.conf, then I have a very simple systemd unit:

[Unit]
Description=Restore nftables firewall rules
Before=network-pre.target

[Service]
Type=oneshot
ExecStart=/usr/sbin/nft -f /etc/nftables.conf
ExecStop=/usr/sbin/nft flush table inet filter
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

and finally if I push updates via ansible I simply replace the file and run nft -f /etc/nftables.conf (via ansible; on-change event).