If you select the
Browse option when creating a new document, it will open a window showing the location of the Document profiles.
On the Mac it's in
users/[you]/Library/Application Support/Adobe/Adobe Illustrator XX/en_us (or your language)/New Document Profiles
If you create a document, set it up however you want in terms of color space, number of artboards, etc. and save as to that same location it will be seen in the drop down for
Profile:. In the image below, I created the "3-Up" document and just saved it to the proper location.
The overall document structure is saved, including number of artboards, color space, DRES ppi, Preview mode - basically anything in the "New Document" windows will be retained by saving the file after it is created.
This procedure works fine in CS6 or newer. I can't say for certain if it works in previous versions. I do not have them loaded to test.