OK, the main reasons for the BTAS redesign was (1) because when it was moved the the WB, they wanted something else with the package other than re-runs or even new shows. they wanted to be special, I guess. One of the other main reasons was that it was the way Bruce Timm wanted it all along, especially the angular-ness (sp?) of the girls, Ivy in particualr. Also, i remeber him once saying a small factor was that the WB wanted a more cartoony look to the series.
As for Catwoman, what happened was the mainstream fans were complining about her being blonde (Fox wanted Selina to be blonde because of Returns), and Bruce and the rest of the ppl on the series agreed to give her black hair. They didnt want her to be a total copy of the mainstream, so they chopped all the hair off. You can read the character explanation in Batman Gotham ADV #4, and You Scratch my back shed a bit of light.