To achieve what you want you need to create your own runtime pak download and mounting system and then swap the assets at runtime using those either BP or C++ examples.
Runtime pak fles mounting seems to be a bit difficult and some discussion threads might help:
https://answers.unrealengine.com/que…runtime-1.html
https://answers.unrealengine.com/que…unted-pak.html
https://answers.unrealengine.com/que…t-runtime.html