If you activate the ULTIMATE plan while you already have an active PRO plan, the PRO plan will be temporarily frozen. This means the PRO plan will pause for the duration of your ULTIMATE plan. The same goes if you activate the PRO plan while you have the ULTIMATE active.
When the ULTIMATE plan expires, you will go back to your remaining PRO plan if it was active before you activated the ULTIMATE plan. If you have a Lifetime PRO VAG plan, you'll return to that instead.