The commissioner can use the commissioner tools to edit the lineups of all teams that join a Custom League. This includes adding/dropping players and moving players between bench and active positions.

All changes made using the commissioner tools apply to games played the following day, unless your league allows weekly roster moves only. It isn't possible for the commissioner to make day-of-game lineup changes using the commish tools.

Similarly, it is not possible for the commissioner to edit lineups retroactively.

After the draft has been completed, it is not possible to remove teams from the league.

Controlling Dormant Teams
Yahoo! Sports does not reassign dormant teams to a new Yahoo! ID. You can control dormant teams using the commissioner tools, but it isn't possible to assign that team to a new Yahoo! ID.