It is certainly possible to downgrade the licenses technically without causing any disruption. The process is to purchase the P1 licenses and then unassign the P2 licenses and then assign the P1 licenses.
However, depending on a number of factors you may be committed to a 1 year agreement on the P2 licenses at this point, especially if you purchases these licenses more than 72 hours ago.
I will refer you to this page for more information: https://learn.microsoft.com/en-us/microsoft-365/commerce/subscriptions/cancel-your-subscription?view=o365-worldwide