If you want a list of current people on your thread, or a list of local events, anything that will need periodic updating, then it needs to be in a BYC article, which you can create in our Learning Center at the top of the page. This is the only way you will be able to edit it after a short period of time. Whoever creates the article can designate whoever they want as able to edit it -- and as many people as they want. You may want a link to your article in the first post of this thread.
BYC has no limitation on how many state threads you participate in. You are always free to post in any thread you choose on BYC. There is no requirement for a list of "state thread members" as you describe, and certainly, not all state threads maintain such a list.
While we don't have a dropdown as suggested above, we do have a list of the state threads in the sticky at the top of this forum. I believe some parts of the country have regions other than the state. There are separate threads for northern and southern CA, for example. At any rate, we have no requirements or limits on this. "State threads" are simply something the people in that state agree among themselves to have.
Feel free to PM me, or any other staff member, or report a post, if you have other questions.