Thanks, appreciate the help guys, but I was unclear in my question, sorry, I'm very new to AS. I just need the cap plate on the lower column. The base plate (and bolts) on the upper column will be in a different (future) model.

I've built the splice by adding a column and using the solutions you've provided. I can set the upper column to "not used" for everything, and place the column, upper plate and bolts on a special (no plot) layer so it "looks" right, but the upper plate and bolts still show in the BOM. Is there a way to mark the upper plate and bolts as "not used" or "future" so they don't show up anywhere?
or
I can delete those parts of the connection leaving myself with just the cap plate, but that deletes the bolt holes as well so I have to add holes. But then it isn't a "connection", its just a plate with holes. I can copy it around (as long as I make sure to grab all the parts like the column shortening feature) but that isn't as user friendly as duplicating a "connection". Is there a way to make those parts a "connection" for future use?? As I said, I'm very new to the application, so I'm just trying to figure out work flows.