The NBA sends ESPN an updated list of every player's position eligibility, including rookies, prior to the start of each season.
ESPN reserves the right to designate a different position for a player.
Once the season has begun, ESPN cannot change the primary position. However, a player can gain additional eligibility for other positions during the season if circumstances warrant it. *
League Managers DO NOT have the ability to change a player's position.
* Under certain circumstances, ESPN reserves the right to change a player’s primary position.
NOTE: It's important to note that roster minimums and maximums within your league's settings relate to the primary position only (the first position listed next to a player), not any secondary positions granted.