Have an option to unselect all plays in a playbook. In preseason I like to use plays I normally wouldn't use. It's a grueling process to unclick each play so I can pick new plays

You can click the button at the top left that says "Clear selection." That clears out everything from that particular tab.

Yes like jlyman said.

You can also save yourself a pre-season playbook to load for the pre-season and save a regular season to load for the regular season.

I like to save a pre-season playbook and for regular season or playoffs, two for each team I play, with two different strategies. Although some are duplicated between teams you can make adjustments as you go and have it organized and easy to remember. When the Eagles game is up for example I just load up one of the two Eagles playbooks I have saved. Make whatever adjustments I what to do for the game and done. Others can have it broken down differently but you get the idea.