I have a movie instance which includes multiple layers, with a fair amount of user customization that has occured.... (color changes, text, etc)
How can I create an exact copy of that instance in another location at the root level?
click and drag select all the frames, right click on them, click copy frames then go to the other location and paste it on the timeline.
If that is what you mean by 'movie instance'
A better way however would just to put all those frames in a movieclip, and then copy and paste the movieclip on the main timeline (_root).
You can attach and play movieclips using actionscript when you want, but your question and description is a bit ambiguous: 'another location' ?
You can create a new instance of a symbol using duplicateMovieClip() or attachMovie(), but creating an exact copy of it that has the same user-made customizations made to it will require keeping track of the changes and applying those same changes to the new instance after it has been created.