How to go through the Chrome login page using Headless Chrome and output a lot of DOM?

I'm trying to accomplish two things with new Chrome without Chrome:

1) import existing Chrome cookies into Headless. Either using a similar method to wget "--save-cookies cookie.txt" or some other means.

2) when I dump the dom (using --dump-dom) I would like the output not to overwrite the existing output file. I have been struggling with this for a while and hope someone can point me in the right direction!