Hi Zyth23, I also looked for a solution for this and found this great Epic Game Tutorial for Modular Character: Working with Modular Characters | Unreal Engine Documentation
As described in the tutorial, the “Mesh Merge” solution should be also capable of using physics after merge. Your solution using MasterPoseComponent is also part of the tutorial, but this solution is described as not working fine with physics.
But when I use the “mesh merge” solution with the c++ code, I even can’t activate physics on the merged mesh. Any idea why? Did you give it a try and bring it to work fine?