There's very little to stop such forking from taking place. There are international treaties in place between many countries to recognize IP rights granted by other treaty participants, but I'm sure there are countries that are not signatories to such treaties (generally they are poorer countries that see being a signatory as being a disadvantage, something I think they are probably right about).
In such a case, where the fork is being operated in one or more countries that don't recognize the IP rights, the countries that abide by those IP treaties could enact laws preventing their residents from connecting to and using such networks, but they wouldn't legally be able to stop the entire network from operating.
Also, it's worth noting that if they (e.g. the US) did pass legislation of this sort, it would be very difficult to enforce, and probably drive such currencies to a black market.
It seems like one of those situations where something gets more complicated whenever we try to "simplify" it.
I mean, crypto space as a whole thrives off a high level of anonymity from both users and developers.
People generally come here because they want to get away from governments, laws, policies and whatnot. This leads to a question, do people have to go through KYC registration before making a fork? I ask because I wonder what the basis is for "legally" protecting your product against people that you technically can't even track.
No, under current US law (or laws in any country I'm aware of ), there's no requirement to register either yourself or other users of a cryptocurrency fork. Cryptocurrency network node operators are not currently considered money transmitters, so no KYC collection requirement exists for them.
Therefore attempting to "protect" one's software from forking becomes an exercise in futility, at least for the case of forking.