When the Hadith is authentic then that is my Madhab

Technically speaking, all that is required for a person faced by such a situation is that his practice be based upon the ijtihad of a valid mujtahid.

I cant comment on the Shafi' Madhab, but I appreciate and understand what you are trying to say. However, this stuff is for scholars of the highest caliber, not for us to research and debate. There is space for change and no one is denying that and what Mufti Taha Karan states is the same for any Madhab, as long as the research and findings are upon the works of Mujtahid Imams. No one is questioning that!

What we are trying to say is that there "WE" are not capable of doing so! That's why WE leave this work for the scholars and they come to a unanimous decision. This is very common especially for new Masaa'il, whereas older issues have remained more or less intact and the same from the start as it is backed by Quran and Hadith. We obviously are not qualified to discuss their Dalaael in full, but can see where they are getting it from with the help of Ulama.

Also, this type of research can only be done by a Faqih and not just a Muhaddith because a Muhaddith is not a Faqih and a Faqih can not be a Faqih until he surpasses the Muhaddith.

Therefore, I should really be asking if you could name us any living Faqih today or even an Imam who is capable of ijtihaad within his own school using the same rules of his own school.

I think you have understood but just to make it clear, the text you put in bold: "ijtihad of a valid mujtahid." refers to the ijtihad of the four Imams which has reached us i,e the four madhabs.

The other point being discussed in the passage by Imam Nawawi is that by practicing on the hadith contrary to the madhab one cannot now say this is now the madhab of Imam Shafi or I am following the Shafi madhab ( based on the saying When the Hadith is authentic then that is my Madhab).