Why not hard program a list of new civs created by a break up:
Have a generic leaderhead so Canada, NZ, Australia have all same leaderhead.
UK-> Canada, Australia, NZ, South Africa
USA-> CSA, Texas, Hawaii, California Republic
France-> Brittany, Bourbonaise, Corsica, Orleans?
Spain-> Argentina, Mexico, Peru, Venezuela
Portugal-> Brazil, Uruguay, Goa?, Hormuz?
Russia-> Ukraine, Belarus, Chechnya, Moldovia
Austria-Hungary-> Austria, Hungary, Bohemia/Czechoslovakia, Slovenia
India-> Pakistan, Sri Lanka, Bangladesh, Nepal
China -> Shinkiang?, Tibet?, Manchuria, ?
Greece-> Attica, Laconia, Aeolia, Krete
Germany-> Prussia, Saxony, Bavaria, Bremen?
Vikings-> Sweden, Norway, Denmark, Iceland
Incans-> Tihuanco, Nazca, Chimu, Tupi?
Indonesia -> Timor Leste, Malaysia, Singapore, Brunei Darsalaam
and the list goes on...