Deactivate reply from user after ticket submission

Hello,
is it possibile to deactivate the reply field for support users after they submitted a ticket? I’d like to disable this option, and make it available again only once a support agent replied to the ticket.
Instead of the reply field, I’d like to have a message like “A support agent is going to answer to your question soon. You’ll be able to ask additional questions about this ticket one they’ll reply”.