Hi,

The answer to your air mixture screw question is YES.

It is made of a separate type material from the fitting its in. Nothing holds it per say as in not crimped into place like many parts of other car in the future of this machine. You can work on it.
I have had mine out on my 1978 B21F. Done it maybe once in the car’s lifetime.
About all you can do is clear any air entry ports and wipe off of carbon or oil deposits.
The screw has a blunt but conical end. Simplistic as a carburetor’s fuel leakage screws.

I gather you are wanting to be through this since it’s an aged car and could have an issues in there somewhere.
A Cleaner throttle body is closer to an original breathing hole that it came with new. (:)
Don’t forget to think about an intake gasket if its original too. Easy to lay back and change.

Have you had a K jet system before or had this car for sometime?
Are you just doing maintenance or having an issue with idle speeds when cold versus at operating temperatures?
My 1978 GT has many mechanically set items and that black knob is only used on the K jets.
I’m asking to find out if you are familiar with setting that throttle body and the auxiliary air valve per a service manuals instructions?
These systems were preludes of lots of experimentation but done to overcome a carburetor’s morning emission issues.
These times were before “buzz words” took over or “hybrids” were introduced by every white coat mechanic available to every company.

No questions or statements are obscure here. (:-)

Phil