[chiph]

>> Let any part of what is now California cease being part of the union.

That's an interesting point. If five new states are created, do they have to petition the United States to become part of the Union?

>> Assign twelve senators to what is now California.

The other states will likely object to this, as it will be a reduction in their own voting power in the Senate. Aside from the "joining the Union" part though, I don't think they have any say in it.

[dragonwriter]

> If five new states are created, do they have to petition the United States to become part of the Union?

For five new states to be created by removing territory from an existing state, the split would have to be approved by Congress; the new states don't have to be admitted to the Union separately from Congressional permission for them to create them in the first place -- allowing them to be created would admit them to the Union.