Does submitting a large list request change your sending limit automatically or do I have to wait for confirmation?

Do you mean a list of requests attached to a forum post, or something else.
You can attach files up to 2MB (I think that is the limit) here in the forum.

You can also paste such a list into a forum post. I've never heard of any lim its to that.

https://get-red.coffeecup.com/forms/large-list-request/
I submitted this form