Do these settings help, i tested this one and appears to hide the result.  

Another option is to open each of the new pages that have been replaced, then go to page history and select the date before the import. But this probably wont work for other items like discussions, as...

Not sure, but is it 'Collaborations' in the main menu, and is this visible for students? Or is it within canvas group homepage area? You might need to add a screen shot so we can better understand the...

One option might be to hide quizzes in the menu. Then post a link to the pop quiz via an announcement - use the delay feature in the announcement, then there is no other way to see it. I think that wi...

Might be easier to put in a module then use the module to unlock at a specific time.

Another option is to open each of the new pages that have been replaced, then go to page history and select the date before the import. But this probably wont work for other items like discussions, as...

Looks like it's not possible (at the moment) - https://support.google.com/edu/classroom/thread/81229268/how-can-i-copy-a-slides-presentation-from-a-published-link?hl=en

I think you might be looking for this. Hope that helps, you can also download in a spreadsheet.  

In discussion select Post to - then choose which section. Then student only access one discussion.

Do these settings help, i tested this one and appears to hide the result.