Can a BS map/mark the sentinel nodes for removal after MX?

Yes, this can be done.  There are two methods for marking the SN that I know of...one carries a dye and the other a radioactive compound.  The dye is blue and lasts 24-36 hours, the radioactive compound stays in your system longer. The point being that this will depend on the speed of the pathology report.  If your BS uses dye, and it will clear the system before the path report comes back, it is possible to put a clip at the SN like you had with the stereoscopic biopsy to find the area after the fact.    

A SNB marks the node that the cancer first "drains" to. There are many nodes in your lymphatic system and typically there is the initial node that is impacted by drainage from the breast area, which is why the dye or radioactive substance is placed before. It first needs to work and then second the BS can find the node or in some instances "nodes" during surgery. The premise is that if the sentinel node or first node is cancer free, then the ones "behind" it will be too because the cancer goes through/to the sentinel node first.

If you remove a breast then there is no way to do this process...1) there is no breast to inject and track the dye/radioactive isotope 2) if you take the breast without doing a SNB and an invasive cancer is found (like in my situation a microinvasion was found that was not detected on my biopsy that said my 3cm spot was lobular neoplasia, but it was not or rather a small micro measure of it was not) then there is no way to tell which node is the first node that the cancer "drains" to or would move to initially. At this point an entire lypmh node disection of that area would most likely be necessary to truly check if any cancer cell slipped through and left the breast and is now cruising through the lymphatic system.