BigMinnie no, no extension does this at this time.
Theoretically yes, it would be possible to create per-tag settings for time frames, but I don't know of any extension that tried implementing it for any kind of setting.
"Allow post editing" isn't actually a permission, it's just a setting that has been placed on the permission screen. So it's not compatible with per-tag restrictions out of the box. An extension would not only have to change the UI to allow selecting a value per tag, it would also need to create the logic that will check the corresponding setting based on the discussion tags.
