Once you register your team for the next season, you can easily "copy" over the rosters from previous seasons. From the My Dashboard page, click "Manage or add players" link next to the team you're adding player to, then click the orange "Copy Players" button at the top. From the drop-down, select the team to copy from, select the players to copy, then click "invite". This will populate the invite section at the bottom of the page--hit "start" to initiate the invitation process.