These characters belong to the Tremblays, Lance Falk, and the other series writers. Any changes or additions are solely their responsibility.
People can and do change over time, but we need to be careful not to shift them too dramatically, because they're not OUR characters. They were made by someone else, and it's their vision. If they want to change it, fine. It's not our place to say.
As both a fan and an aspiring creator, I can see both sides of this issue.
On the one hand, Erico is right. The Tremblays are the creators and owners of SWAT Kats, not us. They should strive to make the best show possible (they do), and be nice to the fans (they are), and you could argue that they really don't owe us anything else. By the same token, we should strive to have a good rapport with the Tremblays and their collaborators (which we do) and not be too pushy or demanding in our dealings with them (which we aren't, AFAIK). Fortunately, the relationship has been characterized by mutual respect.
So where does that leave us when we have suggestions for Revolution? And what if those suggestions are potentially controversial, such as the idea of an LGBT character in what is essentially a kids' show? (As much as many of us [including me] would love to see this happen, we have to be aware that it's a long shot.) Ideally, the process would go like this:
1. The fans make their suggestion respectfully.
2. The Tremblays seriously consider the suggestion, then make their decision.
3. If they decide in our favor, hooray! Everybody's happy!
4. If they decide against us, they explain why in full.
5. If we agree that they had good reasons for deciding against us, everybody moves on.
6. If we think they didn't have good reasons, the discussion continues--respectfully--until everyone is satisfied.