This is a simple, hacky little python script for converting Evermotion VRay MDL materials to MaterialX USD materials.
Pass the script a path to either an MDL file or a directory containing multiple MDL files and it will save out USD files next to the input files with the same names.
Sublayer in the USD assembly and reference all of the USD materials over the existing ones. i.e. via a Reference LOP in Houdini with a glob pattern ("*.usd"). The MDL material connections will remain intact as the MaterialX materials will overlay as an alternative render delegate option.