My understanding is that when you exchange the table with the created partition(maxvalue) all the data will be in just one partition.

Hope this will help..

You rename the nonpartition table.
Create a new partition table.
If u dont need the data from the old nonpartition table to be in the new partition table right away then schedule the inserts on a lean time.

Also take note of some triggers, sequence..etc on the old tables. In some cases u have to disable first the triggers before inserting..