I think it's best to choose the method that you enjoy the most.
The processor unit of Ultradimension Whiteheart (W11 C) is a hidden treasure of Uwii Ruins, so I don't think you can get it until a long time later.
If you want to play the game with the model you're editing, try swapping Hyperdimension Whiteheart with Ultradimension's ism2 model and textures.
I haven't actually swapped models, but both are Whitehearts, so that seems to work.
EDIT:
Since there are differences in the bone positions of the fingers, simply replacing the model and textures may cause the finger shape to be strange.
In that case, I think that the problem will be solved if you replace all the motion files as well.