We have slow response problem in our wordpress apps. We think of upgrading to P2v2 but if that doesn't solve our issue we need to downgrade back to P1v2 again. So we don't want to get stuck with P2v2.
Yes you can downgrade. You can even go down to the free tier, if you don't use any premium features.
Tipp: If you are unsure about such things, just create a new App Service Plan. It only takes 2-3 minutes to create a P2V1 plan. And having that plan exist for a couple of minutes costs almost nothing.