Years ago when we were helping Knight with the rosters we used to send to each other player files. We would basically download them to a USB stick, zip them into a single file, and then send them as an e-mail attachment. On the other end the person would unzip them and then use a USB stick to upload them to their PS4.
I would think the same procedure would work with custom teams with the caveat that the game has a 30 custom team limit.
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