I read and re-read this, and I guess I don't understand what you are trying to do. If the documents are actually identical except for this extra layer, you would get the same result by just duplicating the file that has the layer.
Can you explain more thoroughly what you are trying to accomplish with moving this layer?
In an effort to simplify my question and problem I miscommunicated.
--I have a full-color document (a student manual)
--I have the same document except it's black and white WITH an answer layer (a teacher manual)
I've received a request from my client to put the answers from the teacher manual answer layer into the student manual. So, my question is there a way to move the answer layer from one document into another document?
Please accept my apology for the confusing question. I hope this clarifies a bit.
I understand now. This may be scriptable, but you'd have to ask that in the scripting forum--it's out of my area. I do have a potential solution for creating these documents in the future. In newer versions of InDesign, you can output a black-and-white PDF from your color file. (CS6 for sure; I don't know how far back this goes).
You could create just one InDesign document, and make different PDF files from it to send to print.