I've made a couple of changes after the fact, but pretty much just to format and how the story was divided into parts. I wouldn't go back and make any major changes, which is part of the reason I actually decided to do a web series. I wanted to write something that I as a reader would enjoy (because doing so is when I have the most fun writing), and sometimes my tastes can verge a bit on the dramatic or soap-operay. Because of that I often second guess myself when I'm writing, I imagine what the people I know will think when they read a plot point, will they think it's silly? Somehow I can end up getting a bit embarrassed and so I take out whatever the plot point is and put in something else.
I once learned a lesson that in retrospect might not have been a very good one: if I'm having too much fun writing a particular plot, it's probably not a very good one.
But I realized I write because I love it and enjoy it and not really for other people to read (don't get me wrong, I *love* having people read and enjoy my work, but if all I had were readers who loved my writing and I didn't enjoy doing it I would stop, while I would, and do, write without readers), so really what does it matter if it's melodramatic or over the top or if someone else thinks it's silly, if I'm having a great time writing it. So I started a web series, there were a lot of reasons but part of it was permanence. Honestly there's a plot point coming up soon that in any other format I probably would have changed by now, or just not followed through on. But since it's a web series, and I'm putting it up online, I'm pretty committed to it. I actually went through in my head considering, not seriously but just for the fun of it, if I did want to change that plot thread now, with all the little hints and illusions that have been made to it at this point, what on earth I could change it too, to have it still make sense with what's been said. And I came up with nothing. I'm committed, for better or for worse, to writing the story I want to write. And that's actually something I kind of love about the format of web serials.
That being said I might go back and make a few minor changes to some earlier chapters at some point. For instance there is one line that could hint either at my main character's mother being dead or divorced. I was going for dead. However I have since written a dead sister into her back story, so a dead mother would seem rather excessive on top of that. I'd feel like Lady Bracknell from the Importance of Being Earnest when she says:
'To lose one parent, Mr. Worthing, may be regarded as a misfortune; to lose both looks like carelessness.'.
To lose two close female family members would be very careless.
I never said the mother was dead, just in one line it's mentioned that some people go to church with the main character's father, which sort of begs the question what about the mother? But doesn't actually say she's dead, so I wouldn't feel it too huge if I go back and just throw in her mother into that line as well. Still considering what I want to do with her parents as a whole though so haven't done it yet.
I do have a plot outline written for the first 'book', I have diverged from it a bit but I'm very happy I have it and find it helps a lot and has saved me from making some mistakes that could have gotten be stuck.