According to Catherine Sutherland, there were plans for her to reprise her role as Kat, but this was scrapped because of the cost of flying her out to New Zealand. Presumably, she would have been Tommy's wife and likely filled Hayley's role.
Jason Lee Scott (Austin St. John) was originally considered to be the Black Dino Ranger, but, due to Tommy's popularity (and possibly because Jason had previously played a Black Ranger), Tommy was chosen instead.
The reason for the White Ranger Clone is because in the Japanese series Bakuryu Sentai Abaranger, which the action footage in this show is taken from, the White Ranger spends most of the season as a villain who fighting the heroes. By adding a clone version of the character, the show could use the footage of said fights even after the character had turned good.
According to some sources, Zeltrax's real identity was supposed to be Billy Cranston. But they couldn't get David Yost to return, so a new character was created.
In the first episode, the kids read Tommy's address as 1992 Valencia Road. Tommy was a character on the original Power Rangers, which which began pre-production in 1992 and was shot in Valencia, California.