In the case of a non-resident, then all you need is to get an International Certificate of Competence - I think the US equivalent, which I think is called an International Proficiency Certificate from the ASA ( https://asa.com/certifications/ ), should also be accepted
To the best of my knowledge, it is still the case that only DE, F, I and A qualifications can be swapped for the Swiss D or A-Schein (sailing or motor respectively), and I have a feeling at least the sailing needs you to take the theory test for existing certificates from all four countries, and motor requires a new theory test for two of the four countries.
Well, thats the thing I mentioned: Friend of mine and me are both German, both have a motor "SBF" from Germany... I had to retake theory in SZ, he just paid some fee in ZH and got the Swiss one.
Thank you, sounds like a pragmatic approach - can you please clarify where exactly I can get access to this "VKS tool"? Much appreciated.