Oh, Caledonia definitely Rebel, no doubt about it... As you can see several posts above, I did pretty much what you ask for: Dumnonum and Ordovicii instead of Silurii. Now it's only a matter of cleaning up the details. Do you agree that the capital of Ordovicii should be in Mona? And what about the capital of the Dumnons: according to his: http://www.roman-britain.org/tribes/dumnonii.htm , we have at least two possible places, either Isca Dumnonum (Colchester, but it's later period) or Ictis...
The northern province of England in my map is Brigantes... is this ok? Or should it be Coritani with Brigantes as rebels?

BTW, if we consider the Iceni (although I think Trinovantes are enough for the period, they were more important in the earlier years and had similarly significant role in Boadica's uprising) what about Catuvellauni, in their original settlement north of Thames?

Oh, and another thing. There is simple possibility to mark the presence of Belgae on southern shores of Britain (as reported by Caesar). Just use the same RGB color as Belgian province to mark some area on the island. This has no significant effect on gameplay, I think, but would be a nice historical touch...