Is it possible to take geometry created by a construction blueprint and convert the results to a regular collection of items so that it may be edited piecemeal?
Not a collection of items but you can merge them into a single mesh. You can enable that feature from Editor Preferences > Experimental > Actor Merging.
Hmmm. I got a script that makes staircases and I wanted to delete/alter a couple of the steps just to get some variation.