I don't feel that a writer should have to strictly stick with the way Lois and Clark was written.
I don't think so either, BUT I think the decision to make changes to characterization should come from an informed position, where the author says, I know Lois was actually THAT way, as per episodes x, y, and z, but I'm going to make her a little more THIS way, and I'm going to explain the change by saying that she was actually orphaned when she was two or married to someone else during college or whatever it takes to explain your alterations.
Readers of fan fiction KNOW these characters, and they come to every story with certain expectations based on what they know. Some are unwilling or unable to embrace characterization changes/AU scenarios at all, while others are willing to accept them if they're explained. Very few fanfiction readers, IMO, are willing to accept characters who don't ring true simply because the author doesn't know what "true" is. And you can usually tell when this is the case.
Admittedly, a lot depends on why you gravitate to fanfiction in the first place. In my case, it's not just because I want to read a good story; I can do that at my library. It's because I want to read a good story
about Lois and Clark - or whatever characters I'm reading about that day. If the characters don't seem like "themselves," or at least like some reasonably extrapolated version of themselves, then it's not fanfiction to me - it's just borrowed names.
So if I want to
write about Lois and Clark and have any hope of the characters ringing true to diehard fans, then I have to know canon well - even the shows that I think are kind of the pits. As a new writer here, I feel that responsibility even more; there are readers here who have "known" these characters for a decade, whereas I've just met them in the last two years. So I have to do my homework, and then, if I want to make major changes, I have to make them in such a way that they seem logical to fans of the show.
Just my .02
Caroline
