Is there a complete & detailled guide to apply downscaling methods (from dowloading data, extracting the area of interest, applying the downscaling procedure to get the final results)?

I don’t think we have a detailed guide within C3S but I believe there are several pages covering downscalaing techniques on the web.

in principle this would be interesting to be done as a toolbox operation. is this maybe planned already?

Yes we are looking at that as an option. The question is the computational complexity of the tools that we can afford on the CDS/DIAS given the possible user-base.