I see. I think in this case I find the description in the Extension store a little misleading, as it states that you can “Add free or paid plans with custom expiration and restrictions.” Maybe this was just me hearing what I wanted to hear, but I got the impression that you could create custom plans with custom restrictions (i.e., restrictions that you can define yourself without being limited to certain features).
Knowing what I know now, I understand the description a little better, but without understanding the way the extension works, I did find it a bit misleading.
In any case, would the code snippet mentioned in this post allow me to achieve what I am trying to do?