How to prevent a particular plugin from being activated?

Hi,

When I created all my templates I used for some of them a plugin that has a huge impact on what the templates look like. For some reason I've changed my mind about this plugin and decided to make it a "premium plugin" (using Pro Sites). But I still use it on the templates.

I've seen that if a user chooses one of these templates this plugin is activated (even if they are free users). Obvisoulsy that makes sense in a way but it's not good for what I want to do :wink:

My problem is that I don't want to change these templates (I'd rather present them as "premium templates" on the registration page, but let free users choose them, to get let's say a "light version" of these).

I'd rather not use the trial option of Pro Sites, the one that let all users test the Pro features during some days or weeks. I'd really want to just prevent this particular plugin from being activated in the first place.

Is this possible? What solution do I have? Maybe by doing a trick on these templates?
Using the Plugin Override Options in the network admin would do the job?

Thanks!

Best Regards