UE4 games made by Bamco (Bandai Namco ICYMI) doesn’t have the modkit provided by the devs yet it manages to have mod applied all over the place, at least cosmetic mods. Especially Soulcalibur 6.
Without the official toolkit/dumbed down UE4 SDK, active modders (those who create mods for your game) will inevitably have to get their hands to UE4 SDK and U4Pak to make/replace custom content especially custom meshes. Passive modders (those who just apply mods to their installation of your game) just have to deal with U4Pak.
If you just want to allow mesh mods or audio mods, or any cosmetic mods, really, you can leave it that way and let the modders do their job with U4Pak and making the cosmetic mod in a fresh UE4 SDK, and you can leave your game in Shipping build then call it a day.
This results you unable to integrate your game with Steam Workshop, but then Grand Theft Auto V is still moddable without Steam Workshop and the mods are collected independently.
On the other hand, if you want to allow custom script to be added to your game, that is where things can get confusing real quick and I’m sure we’re scratching our head around it. The wiki provided by seems to get around this case, but I still don’t know how to obtain the profile in a shipped game or providing the profile in the game files.