As stated in the question I am procedurally generate a planetoid. The low poly planetoid can have lots of spikes and automatic uv mapping isn’t satisfiying (because the algorithm is finding lots of seams, which generated lots of islands and makes LoDs difficult). So I thought I could use vertex colors for albedo. I feel silly never tried using UV-Channels for roughness and metal. After a short search I also found out that the texcoord-node supports the ability to set the uv-channel-index (Can you use a second UV set for a second texture map? - Rendering - Epic Developer Community Forums). Thanks for the nudge 