Hi Shelby,
I don’t know Fusion, but why don’t you simply update that Material directly in Blender (why not do all the Material making and assigning in Blender for that matter)?
In Edit Mode Select the Faces you want to have that new Material and Assign that updated Material to those Faces.
It is normal to do the Modeling in the program you are more comfortable with and the Shading in the program you are Rendering in.
It is also highly recommended, that you know at least a bit about Modeling (and Texturing and Shading and Lighting) in Blender, to be able to fix things that might go wrong (because things going wrong is not uncommon when Importing/Exporting).
