First off you can not import an .obj file to MH,you can only load saved character from within MH which does use on .obj file which is the base mesh but applies the various modifiers.So what are trying to do as there is most likely an other way to do it

You will probably need to do any mesh work in a 3D modeling app such as blender,3Dmax or Maya.The other use for .obj files is for clothing but again you have to use blender to fit the clothing to the model no other way ATM using the blender makeclothes addon.
Enjoy the Choice

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