The fed rule book states that it is a flagrant technical foul if a player participates after changing his/her number without reporting it to the scorer and an official. Does this mean ejection? The book says that rule 10 sec 3 art 9 is also a flagrant T. I can see that as being ejection, but I'm wondering why article 1 warrants ejection if indeed it does.

It is viewed as an unfair attempt to deceive the opponents. Numbers are often the only way opponents can identify players.