You may import your own custom seeding list by using our Bulk Add feature.
In your tournament settings, go to Attendees>Export (the button located in the top right). This will give you a spreadsheet of all of your attendees. Use the column of gamertags that doesn't include prefixes.
Generate your own seeding by ordering your players in a spreadsheet.
Click Bulk Add in the top-right corner of your Attendees page, paste in the list of gamertags in the order you've seeded them, and click Add Players.
In the Match Players tab, you can pair gamertags you've entered to existing smash.gg accounts.
Lastly, choose the event and phase to add the attendees to and choose order of input under Initial seeding.
Note that you can only add up to 50 players at one time. You will need to repeat this process in order to add additional players.