@AllT Just to add to what @Handy1 said: assuming you are able to get access to this "new activations only" plan, then yes, you can typically switch plans with the effective date set to be "at renewal" rather than "immediately". So your new plan wouldn't kick in until your current one is finished, and you won't be paying for both plans at the same time.
EDIT: Ignore crossed-out details and see reply from @Handy1 , apparently when support changes your plan it happens immediately!
