You can't trim them before sizing because they will get longer again when you size them.
And probably some more longer then others.
So, you are back to square one.
Also, the neck turning cutter pilot is a loose fit in an unsized neck and you may get chatter or wobble.
If you are using a progressive press, just size them all in station 1 and trim them & chamfer/debur, then you are ready to load.
Just skip sizing them again.
rc