Gamerule: Hopper Toggle.

While similar ideas have surely been posted (ie at least the hopper lid post I saw when researching this topic), I believe my perspective will be helpful and could introduce some very valuable command abilities for Redstoners.

Complex hopper builds are exceedingly valuable in Minecraft, anywhere between clocks, super smelters, and sorting systems, however for those of us who think moss is prettier than iron we may want to cover these up.  Unfortunately as I recently re-experienced, building isn't always so clean, and losing even a single block into a complex hopper machine can utterly break the Redstone.  Oh, how I wished that I could have toggled the hopper's ability to puck up items.

Now on to how I think the command should work.  There are a few versions provided, as I know a little bit of programming and don't want our lovely Mojang team to suffer too much.

In a bit of a preface I will be assuming that Hoppers have two abilities, that of picking up items in the world, and passing items from inventory to inventory, referred to as pickup and pass respectively. However, I do not know that this is actually how Hoppers work.

Version 1, universal toggle.  Toggles all hopper abilities in every dimension

version 2, conditional toggle, toggles all hoppers with certain conditions (direction/dimension)

version 3, regional toggle, toggles hopper abilities in a specified region (similar to /fill)

version 4, all of the above. allows the player to toggle based on each variable introduced here.