• Blender
  
• Kenshi IO Continued Blender Plugin

• Import pilot mesh into blender with kenshi_io_continued (https://github.com/Kindrad/Kenshi_IO_Continued). A good template is aspilo.mesh
  
• import new mesh data
  
• name UV map of new mesh model same as UV map of the existing pilot mesh(s)
  
• position new mesh next to pilot mesh, adjust scaling/rotation all that, then join them. Leave a little space so you can select the geometry separate from the main pilot still.
  
• Go to edit mode, select vertex group you want to swap mesh data with and delete faces (this deletes pilot mesh data you have selected), then select new geometry and assign it to the same vertex group.

If you want to ADD an object without deleting anything, and the object has its own material, you can do this: join meshes. assign new mesh to vertex group. Then, separate those same vertices by material. Now they have the correct vertex group attached and can have their own material.

If copying in mesh data from another object such as another pilot, you must clear all modifier/vertex group data before adding it to your pilot. Otherwise the exporter will break because it is trying to reference bones or groups that dont exist. Basically you must only copy and add the mesh/material data, nothing else. I found the best way to do this is to open your 2nd object in a different Blender instance, separate the mesh data from bones/vertex groups, then copy paste it into your working Blender session.

• Name materials to what you want for gun/pilot. Delete extra/unused materials from previous imported model if needed.
  
• Export from Blender using Kenshi with these options checked: tangents, apply transofmr, apply modifviers, export skeleton, export animation. Ensure entire pilot/gun is selected when exporting otherwise it wont make a material for everything.
  
• Run that mesh through OgreMeshUpgrader
  
• Open mesh file and change the reference to file.skeleton to aspilo.skeleton unless you have custom/different animations
  
• Throw mesh into your mod, and add materials.