Transferring Bone Weights
This article explains how to transfer weights from the old mesh to the new one. This is a simple way of transferring the old mesh's rigging to the new one.
It is recommended to follow the instructions in the Replacing Simple Meshes guide before trying to transfer weights. We will assume that the new mesh has been added as a child to the NUD object, and has an armature modifier using the same armature as the old mesh.
In order to correctly transfer weights, both meshes have to be aligned. When transferring weights, all of the rigging from the old mesh's vertices will be copied to the new mesh's vertices, and this will happen for all vertices that are near each other.
While aligning the meshes, you can change the old mesh's pose to make it align with the new mesh. This should be done only for transferring weights. After the weight transfer is done, you can change the old mesh's pose back.
Switch to Weight Paint mode with the new mesh selected. Then, click on the old mesh. If done correctly, the selection of the meshes should look like this, with the new mesh selected with a light orange color, and the old mesh selected with a dark orange color:
Next, from the Weights menu on the top left in Weight Paint mode, select Transfer Weights:
After doing so, a new tab will show on the bottom left:
Click on it to expand, and change the Source Layers Selection option to By Name:
If everything was done correctly, the new mesh will now have the old mesh's weighting with all vertex groups:
