Ummm. Not entirely sure what your question is, so I'll have stab.
Extension 1 won't effect what you do for Advanced at all.
Your exam will be Paper 1: Journey (which standard and advanced students all do, irrelevent of whether they are in ext 1 or not)
Then Paper 2 which is where students are split up. The advanced and standard students sit an entirely different exam. Once again this is irrelevent of whether you are in ext 1.
I made that way more complicated then it actually is.
cheers