Hey Sam, I have a video that discusses this.
Creating RGBW, RGBL, or RGBA fixtures in UE5 with DMX Control
Essentially you need to break normalized attributes, find all your existing channels, like RGB, and then find your “extra” colors normalized values, multiply those by a vector RGB that represents the color you were emulating, and then add that to your RGB vector.
You do not have to pass in values with a max of one, you can go over one and rendering will be just fine.
Once you add in your extra values, break that factor, and pass all of those into a “make map” (values per attribute map) node.
Another thing is that you do not have to add new attributes in your project settings, and as I found out, after adding six attributes, this slowed my project down to a broken state.
You can simply go to the DMX profile, add an attribute, click on the attribute name, and type in whatever attribute you want. Then type that Same name exactly into the fine attribute, and it will find it successfully.