I always ask our purchasers to put a note on the PO to any shops that we send 3d models to that states that the prints are the controlling documents and that is what the final parts will be inspected against. There have been times when the 3d model was the controlling document, normally for 3D...
Do you need to open the part file to rename it? I ran into a similar issue, not renaming though, and it turned out that I needed to open the file in order to make the change.
Can you just select the part and save a screenshot somewhere that you then insert into your picturebox, all using code? You might also be able to save the screen as a jpeg in SW.
Are you sure you are not trying to use more tokens than you have available? That has bitten me a couple times. It will just sit there with no warning or errors.
Not knowing the application maybe this is not a reasonable question but here it is: Could you swap A&B in your PLTZF, then you could keep B in the FRTZF. Or even add A to you FRTZF, though this might be a little more than you really want/need.
One way you could do it is to create a cutting feature (i.e. extruded or revolve cut) in the assembly that is shaped so that it cuts out everything that you don't want. Then the mass properties will give you the info for what is left.
I don't think just adding B will do anything. Position is probably better but I think you can change this to angularity and then use A&C, or if you are more interested in the udim'd other slot you can use that instead of C
For question #1 & #2: Here is a link that goes through a basic description, https://simulation-blog.technia.com/simulation/implicit-vs-explicit-finite-element-analysis. The help file has more detail.
This might be moot if you go with shells but you can also partition it into smaller, more regularly shaped areas/volumes that will mesh better. That will definitely help.