I've added some information about swapping unit parts from one model to another in Blender to the wiki in Blender Hints and Tips. That should apply to any unit type converted to .dae by IWTE and also to RR units converted using Feral's CasConv.exe to .fbx


(some things like how to join parts without losing the UVs come up quite frequently, and I can never find the info to link to...)