Yes, using API Scripting:
Dashboard -> s2Member ->API/Scriptiong -> Simple/Shortcode Conditionals
On your page put the “trial” form inside a shortcode like this
[s2If !is_user_logged_in()]
and the “paid” form inside a shortcode like
[s2If is_user_logged_in()]
This will make it so that if the user has an account on the system they will be shown the “paid” form and if they do not they will be shown the “trial” form.
Note: People will still be able to get around it by creating new accounts but there is not much we can do about that with this software.
Put together the page would look something like this:
[s2If is_user_logged_in()]
//Content for users who already have an account in the system goes here.
[s2Member-Pro-PayPal-Form level="2" ccaps="" desc="$20 USD / Monthly (recurring charge, for ongoing access)" ps="paypal" lc="" cc="USD" dg="0" ns="1" custom="pursuitathleticperformance.com" ta="0" tp="0" tt="D" ra="20" rp="1" rt="M" rr="1" rrt="" rra="2" accept="paypal,visa,mastercard,amex,discover,maestro,solo" accept_via_paypal="paypal" coupon="" accept_coupons="0" default_country_code="" captcha="0" /][/s2If]
[s2If !is_user_logged_in()]
//Content for people who are new to the site goes here.
[s2Member-Pro-PayPal-Form level="2" ccaps="" desc="30 Days free / then $20 USD / Monthly (recurring charge, for ongoing access)" ps="paypal" lc="" cc="USD" dg="0" ns="1" custom="pursuitathleticperformance.com" ta="0" tp="30" tt="D" ra="20" rp="1" rt="M" rr="1" rrt="" rra="2" accept="paypal,visa,mastercard,amex,discover,maestro,solo" accept_via_paypal="paypal" coupon="" accept_coupons="0" default_country_code="" captcha="0" /]
[/s2If]