Can I decide if a new client is subscribed to autoresponders or not?

Yes, anytime you create a new Active client, or change a Prospect to Active you will receive a pop-up window letting you know that your new client will be subscribed to your new client autoresponder(s) and ask if you are sure you want them to receive this. See screenshot below.

If you click "Yes" then your new client will be subscribed and receive your new client autoresponder(s).

If you click "No" then your clients will not be subscribed or receive any autoresponder(s) from you.