[ossiblue]

I'm certainly no expert on CIS but from my limited experience, having to adjust the mixture screw bi-annually usually means there are other issues that have not been addressed. Porsche provided a plug for that screw for a purpose. That is not to say your mixture doesn't need adjusting, but once it's set, and if the rest of the system is in spec, it should not have to be touched for "changing atmospheric conditions" (unless, perhaps, you are moving to/from altitude.)

You certainly know your car better than I, and I don't question your knowledge of it's workings. I am only offering my insight from my own experiences and the suspicion that continually adjusting the mixture screw is covering up another problem.