Based on what I can make sense of, you would want a rule more like this one?
2018959 “\\$EXTERNAL_NET any -> \\$HOME_NET any” “[$EXTERNAL_NET,!$EXTERNAL_IP] any -> [$HOME_NET,!10.0.0.3] any”
The unsaid detail here so far is that you have to set/automate the finding and setting of this External IP into the new EXTERNAL_IP variable that you will setup in your suricata.yaml or custom.yaml file
The automation of this can be via a script that would allow you to find your Public (External) IP and then modify the line for EXTERNAL_IP to be that value via a CLI tool like ‘sed’
Currently, I have manually modified my $HOME_NET to include my IPv6 Subnets, but I have not automated this modification yet mainly because of the complexity in pulling it off (and thankfully my IPv6 subnets have not shifted too quickly) but I should be able to use my router’s API to get that detail, update the source file and copy-over if it has changed and either soft re-load or service restart Suricata