Let's take a look at each of these components and explore their importance: These components make up the body, face, hair, and clothes. Unlike the default UE4 Mannequin character, which is made up of a single Skeleton and Geometry Mesh with a couple of game-specific components set up in a Blueprint, the MetaHumans are made up of many different components. MetaHumans Blueprint and Their Components For example, BP_metahuman_001 is the female MetaHuman. The metahuman_ folders contain a Blueprint of a MetaHuman character. Some clothing is not common to all MetaHumans and, therefore, is stored in the Sample folder instead of the Common folder. You can find it located in the Content/SampleMetaHumans/Common/Female/Medium/NormalWeight/Body folder. This simplifies using the MetaHuman characters with animations and set up. Other things to note with the MetaHumans folder organization and structure include:ДЄll MetaHumans use the same Skeleton Asset ( metahuman_base_skel). For example, the female character is stored in the metahuman_001, and the male in metahuman_004. You will find files used for both MetaHuman characters stored in the SampleMetaHuman/Common folder, while assets unique to each individual MetaHuman are stored in one of the corresponding metahuman_ folders. This folder contains a set of core content that is common to all MetaHumans, whether male or female. In this project, the MetaHuman characters are found in the SampleMetaHumans folder: Whether you are looking at this sample project or creating your own characters through the MetaHuman Creator and sending them to Unreal Engine, they are all stored within their own folder for ease of reference and access. MetaHumans files are stored in a MetaHumans folder, similarly to how the files for the UE4 Mannequin found in some of the engine's template projects (like the ThirdPerson Template) are stored. Take a look at the core components that make up our MetaHuman characters and how you can start using them with your own projects. MetaHumans are much more than a collection of parts brought into Unreal Engine they are designed with thought and care to simplify the creation process and enable creatives to start generating content within the engine quickly. MetaHumans created there can be downloaded through Quixel Bridge, directly into Unreal Engine, with only a few clicks-like any of the thousands of other assets found there. What is a MetaHuman?ДЄ MetaHuman is a high-quality digital character that is created in the Unreal Engine online application MetaHuman Creator. The project will not look as intended, but you can still explore how the content is set up. Selecting the rig and entering edit mode you can add new bones, and parent them to the rest of the rig you will have to create a new vertex group in the character's mesh, with the same name as the new bone, and assign a weight to the vertexes you want to move, for having it deforming the mesh.Д¬onsider also that you can parent more than one mesh to the same rig, even if this solution is not the best, often.While it is possible to open and run this project without the recommended hardware specifications above, the lighting and features of the project are designed with these in mind. A lot of problems generally can come out when shapeKeys are involved (all the face, in your case), in which case the new vertexes can seem to move in weird ways: any vertex modification in this zone probably will need a lot of adjustements in every Shape-Key in which it is involved. Viceversa, if you extrude a vertex from another, it will copy the properties of the previous active one: if the new vertex stays in a similar position, very often there are no problems. Maybe you should start from a simplier character, for practicing, until you reach a good comprehension of what is going on.ДЄnyway, all deforming bones are related to vertexes, so you can freely edit their materials and textures, without affecting the rig. The character you've downloaded has 134 bones, some deforming, some used as machinary, some constrained and/or related to other bones, some used with drivers, to perform deformations using a lot of shape-keys, expecially in the face (as usual). There's nothing wrong in the idea of modifying a character which is already rigged, as long as you know what you are doing:

How to edit facial rigs