You would need to create a unique level editor system within your game. The EULA forbids using modified UE4 tools as tools/features for a game.
So, for example, if you had a terrain editor in your game it would have to be completely created by you and not use any of UE4’s landscape editor tools. It could be made through C++ or Blueprints, but could not be directly derived from an already existing engine tool.
You could instead have players use a full version of UE4 to mod the game. Either of those two options would be EULA-compliant; Making a unique level editor or using full UE4.