Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Since you are planning to switch to a subscription with more features, it is possible to add the subscriptions together, assuming of course that you order the new one using the same Microsoft account. See https://support.microsoft.com/en-us/office/switch-between-microsoft-365-subscriptions-3fcc1efc-2722-427f-8efa-db94b9b0a36b#bkmk_morefeatures .
In doing so, it seems that you will lose some days from the subscription, though. See the table below (it is a screen shot of the article).