changing iptables rules when using ipv4.method=shared
There is a lack of information about the iptables operations of NetworkManager in the documentation for ipv4.method=shared. Might be my fault, but I ended up looking through the source to get the information whether the rules are configurable or whether I can disable setting iptables rules at all.
Besides I'd strongly prefer to have iptables rules configurable. The way it works now NetworkManager interferes blindly with whatever firewall rules might already be set.