On a vCMP guest, can i add cores without impacting traffic ?

I read the entire administrator guide for the vCMP system but cannot find this answer.

If i see a guest that's running on '2 cores per slot' has high cpu, can i increase the value to 4 without causing any impact to traffic ?

Or would i have to move to configured state, make my change and then provision and thgen deploy?

Thanks in advance.