Modding games on UE4

I want users to be able to mod my game; how can they? Do they use UnrealEd provided by Epic? Or do we have to create custom made editors - from scratch?

I am planning on doing this in two ways.

  1. Make my game open source.
  2. Tell people that they have to subscribe to the unreal engine 4 in order to mod my game.

Let me elaborate -

Since my game project will be open source on git hub atleast the code will be. people can take blueprints that I have made and improve upon them and even modify and use them for their own Games.

This is really the only way I can do it myself until epic games opens up for official mod tools.