Hi,
You can accomplish this by setting up your security correctly. A paid vs free trial membership could be different user roles. Then on your entities you can have a flag that differentiates between paid vs free content, and then when you setup your access rules on your entity, you can constrict one role to only show free content.
Here is some helpful documentation:
https://docs.mendix.com/refguide/security
https://docs.mendix.com/refguide/access-rules
https://docs.mendix.com/howto/logic-business-rules/define-access-rules-using-xpath
Hope this helps!