Of course you have a say. I don't know where your goinbg to submit it to, but if someone decides they'd like to use it, then you have every right to have an input.
You might want to discuss that, however BEFORE a contract has been drawn up, and then there's always a discussion with the directors and producers of whatever vision you may have for it.
If nothing has been contracted, you can always pull a trick like in the movie 'Phonebook' with Colin Farrel, who plays an agent. You tell the competitor that someone wants your script but you might consider switching to their company if they suit you more.
Or you tell the people who want your script that they'll lose you otherwise...
But anyways, most companies (considering you're talking about your average production company) will definitely want your input on some things, and in good cases, you can also work with the casting director as well. As long as you don't dictate them and realize that they were hired for a reason as well.
Hope this helps,
and Good Luck!
Source(s):
I live, breath, and study film production