I have upgraded a katana to legendary only to discover that none of my mods like crunch or pacifier will be accepted into the mod slots. Is this a bug or are there specific mods for blade weapons?

Lots, but many are outright broken, do not function or can wreck other mods in combination. It's fun Early Access kind of modding.

Thanks Tracido. You wouldn't happen to know of one that works?

Oh not off hand, game is way too broken to just focus anything like mods right now and as far as I'm concerned, I'm using a dev console for everything and not caring about anything the game has structured, what you will have to do is what I do, I sacve the game, mod it, check the stats, and use it in game first, then if it works I save again, if not reload and try again, since the fools made a broken mod system and you can't even take the mods back out.