Is it required that I replace incorrect general/character tags that I remove with other fitting tags? I know that tags in the red invalid category should be replaced with valid tags, but does this rule apply to the other categories like general or character? https://e621.net/help/tags implies that this only applies to invalid.

I think it's something that needs to be approached with a little common sense, if a tag clearly doesn't belong it should be removed. If you can identify the reason the tag was there, like being an obvious typo, I'd have an expectation for people to replace it with the valid tag.

But sometimes tags just feel like they're there for no reason at all, with no obvious reason why anybody would ever put that there. I don't think anybody would get upset if these tags were just plainly removed, but it's always good to try and figure out why it was there. Sometimes looking into it will reveal situations like bad taggers just using the same tags on every image variant they upload, copy/pasting the tags from FurAffinity or other sources that don't enforce strict tagging guidelines, or just repetitive sloppy tagging from certain users.

The same goes for tags in the invalid category, honestly. Sometimes it's just bad tagging and there's nothing to replace it with.

faucet said:
But sometimes tags just feel like they're there for no reason at all, with no obvious reason why anybody would ever put that there. I don't think anybody would get upset if these tags were just plainly removed,

In my current situation I would be simply removing twilight_sparkle_(mlp) from princess_twilight_sparkle_(mlp) posts without finding a replacement tag, because the former tag isn't relevant in alicorn twilight posts.

markhor_screwhorn said:
In my current situation I would be simply removing twilight_sparkle_(mlp) from princess_twilight_sparkle_(mlp) posts without finding a replacement tag, because the former tag isn't relevant in alicorn twilight posts.

In that case the replacement tag would be princess_twilight_sparkle_(mlp), which is already on the post, so that should be fine.