I don't quite get this question...you're free to update as you please if you're writing a fic with multiple parts, and of course one has to make all this up in the first place. o_o?
Kairi, I think he means to ask if he can post a fic that he hasn't completed at the time of posting, and makes up chapters as the fic progresses. In which case I think you can, though I'm not too sure. Don't rely on me, but I believe the answer is yes.
It was as in, As the ideas come into my head, I type them into the fic on the forum/thread, instead of the normal way, typing it out in Word (or other similar program on a computer,) then cut-and-paste-ing it into the post/thread.
If you mean in the fact that you will make use of the editing button, then yes. But if you are just typing it straight into the reply bos, then...? Don't really want to speak for other people, but... I really hope that you can spell correctly. Writing in Word helps with that a bit. I don't know. A couple of people say that you shouldn't just type into the reply box.
If you itnend to check yoursepllings before you post, what's so different about typing it into the reply box aside from typing it into Word? Almost everybody makes the fic up as they go along, they certainly don't plan it out scentance by scentance. If all you intend to write is a bunch of lines that don't make any sense, then no it's not allowed.
Hey, as long as your fic is coherient, it should be fine. A lot of people, when they just type into the reply box, have spelling mistakes running amuck. Since you check before posting... you'll be fine.
The something was a thing my friend said when I asked him this. All he said was "something."
You'll be fine as long as you proof-read before submitting.