Here were the official rules regarding lineups for the Women's NTI - I saw Colette Lewis mention #1 which is why Duke was able to make the changes they did:
Line-up Substitution policy/Rules
1. All teams must play their master line-up two out of the first three matches of the Championship.
2. A singles player and/or doubles team may move one position up or down, but not both, from the master
line-up.
Example: Your #3 player can also play #2 or #4, but not both.
3. Once the match begins, if the line-up is changed due to injury, default or if the doubles is changed because the match has been decided, the master line-up will still be considered played.
4. A submitted line-up will not be considered the master line-up if it was not originally the master line-up but became that in the course of the match.
5. A submitted line-up qualifies as the master line-up as long as the players remain in rank order relative to the original master line-up. For example, if the #3 singles player is held out of play, and everyone moves up, the line-up would be considered the master line-up.
6. In doubles, you may direct line substitute for a sick/injured player as long as the teams are still playing in order of ability. The opposing coach may protest a doubles line-up if he/she feels they are not in order prior to the start of the match.
7. The on-site ITA Games Committee will have final ruling on all on-site protests.
8. Although rotating players is allowed, normal ITA line-up rules still apply: ITA Rule II.H.2."In singles, players
must compete in order of ability, the best player on the team playing at the No.1 position, the second best at No. 2 and so on through all positions. This rule shall also apply to doubles play with the strongest doubles team at No. 1, etc."