The way I do it to freeze apps is using focus mode. You can flag these apps as "distracting" and enter "focus mode". Their icons will turn gray, only run when explicitly opened, and auto-freeze in 5 minutes. After 4 minutes a notification appears to extend this run time. This works for me for most of the cases.

If you didn't tag your app as having Ads, or having in-app-purchases but it is tagged later or released that way all the pre-registrations that happened while not having the appropriate will not be able to auto-install.

For legal reasons, the user needs to know what it is signing up to at the moment that agrees to install (auto-install = deferred install). I think that makes sense but obviously apps become less attractive when those tags are displayed.

I also think the pre-registration program makes sense for games rather than apps.