Houdini UDIM export
This is a tutorial on dealing with a custom UV layout from your digital fashion app when you set them up as UDIMs. I use Houdini in this case, so I imagine if you can translate this to Blender, it might work in a similar way. I don't use Blender for anything UVs, so I don't know. But this is from MD to Houdini to Substance Painter