Short Answer: Yes, Character Customization (Modular Pawn) can be managed through Blueprints, but, it would have to be geared to work with skeletal meshes designed for this purpose, vise versa.
Long Answer: UE4 is designed with modularity in mind and Blueprint Components are ideal for this feature. I’m a huge proponent of modularity and customization for everything. I plan to build a BP setup that works similar to Daz3D Genesis.
There are many techniques for Character Customization/Modular Pawn to include modifying the base mesh with TargetMorphs, snapping external attachments/accessories with Sockets, changing appearance w/ Texture/Material Layers, blending different skeletal animations, assigning different AI behavior with Behavior Trees. Every property can be parametrized and exposed to Blueprints for procedural or manual modification during run-time.
Obviously, with all this flexibility there a many ways to implement such as system, but, its mandatory that the skeletal mesh assets be designed for interchangeability unless unorthodox. I would suspect one of the easiest aesthetic customization features you could get working is attachment/accessories on using skeletal mesh sockets: How to attach BP to skeletal mesh socket.