[officialtony]

In order of priority, here is the rule:

a.)by a player who has never been in the game or a player who has subbed in at that position;

b.)By any legal player on the bench regardless of previous position played.

These are paraphrased but the gist of it is your libero would have been OK if she was on the bench. If she was in the game, she would have to do a replacement and then come in as the execptional sub.

So . . . .

answer to 1. Since #2 was not subbed for previously " a.) " does not apply. As long as you get the Libro to the bench she was OK for the sub;

answer to 2. Absolutely must change jerseys to match the rest of the teammates;

answer to 3. Switching jerseys was not a problem as long as she does it in the locker room or restroom away from the public area.

Sounds like you did OK for not being sure of the rule.

For me, the libero has got to be CLEARLY AND OBVIOUSLY above the net for me to call an illegal attack on her. Also remember, the libero ball must be completely accross the net or legally blocked or attacked by the other team to constitute an " attacked ball " on the libero hit.
Use your best judgment and be consistent and you'll be fine.