I got good news and bad news. The good news is that yes, you can use the PUT v1/op/devices/bulkImport service to update the credentials for a device. That includes switching it to use a credential profile; just specify the device IP, the credential profile, and no other credentials (you can specify UDFs, however). The device will then use that credential profile for all further interaction.
The bad news is that we don't support changing a device's management IP via the API. The service above uses the IP to identify the device to update, and if a new IP is given, it will proceed to add a new device to the inventory.