Oh, I wouldn’t ever suggest that the method does everything its author does - the claims of helping in cancer cases and such are wee bit too “optimistic”.

But the question was concerning the possibility to build up cold immunity. And the answer is “yes”. The method I mentioned absolutely will build up cold’s immunity (or resistance, or tolerance if language purism is a factor) in everyone who will attempt it.

There’s no magic hocus-pocus in it. It’s very simple concept used in many “methods” - Buteyko comes to mind, so does Russian Siberia.