You could try that and make the model ID for the Ragnarök (as it should be spelled
) the same as the Masamune's, but I think they're character specific. Many weapons share similar model IDs, but never on the same character. As the author of WM, I can't guarantee any type of results from this. Certainly try it first, but make sure you know what you've changed it from if it doesn't work. Unless I've been misinformed and that part isn't really model ID, you'd probably be better off with a model editor that you could actually replace Ragnarok's model with the Masamune.
Leviathan might be able to do that. FiceLZS from that same page would at least let you decompress all the models and replace the two.