Hello, I have added this feature to KES (third party extension) today. I believe it is working correctly based on your requirements:
Show an icon next to magazine names on the main thread index (https://kbin.social or https://kbin.social/sub if logged in). Click this icon to "softblock" threads from that magazine from appearing on your main thread index. This does not block the magazine outright: you can still go to the magazine directly, so it is less aggressive than a total block.
Show a Softblock/Unsoftblock button in the sidebar of magazines, as well as in the Magazines index located at https://kbin.social/magazines. As you would expect, this button has the effect of adding/removing a magazine from your filters.
Show a tab at the top of the Magazines index that you can use to centrally manage your softblocked magazines. For the time being, this is merely informational.
Full details can be found in the release notes here over at /m/enhancement.
Let me know if this gives you the functionality you wanted.